Rigidized filler materials for metal matrix composites and precursors to supportive structural refractory molds

ABSTRACT

The present invention relates to a novel process for forming metal matrix composite bodies. Specifically, in a particularly preferred embodiment for making metal matrix composite bodies by a spontaneous infiltration technique, an infiltration enhancer or an infiltration enhancer precursor or an infiltrating atmosphere are in communication with a rigidized filler material or a rigidized preform, at least at some point during the process, which permits molten matrix metal to spontaneously infiltrate the rigidized filler material or riigidized preform. A structural refractory material which holds the preform is made by forming a first precursor to the supportive structural refractory material and subsequently causing the precursor to become a rigid supportive structural member. Such spontaneous infiltration occurs without the requirement for the application of any pressure or vacuum.

DESCRIPTION

1. Technical Field

The present invention relates to a novel process for forming metalmatrix composite bodies. Particularly, in a preferred embodiment of thepresent invention directed to forming metal matrix composites by aspontaneous infiltration technique an infiltration enhancer and/or aninfiltration enhancer precursor and/or an infiltrating atmosphere are incommunication with a rigidized filler material or a rigidized preform,at least at some point during the process, which permits molten matrixmetal to spontaneously infiltrate the rigidized filler material orrigidized preform. Such spontaneous infiltration occurs without therequirement for the application of any pressure or vacuum.

2. Background Art

Composite products comprising a metal matrix and a strengthening orreinforcing phase such as ceramic particulates, whiskers, fibers or thelike, show great promise for a variety of applications because theycombine some of the stiffness and wear resistance of the reinforcingphase with the ductility and toughness of the metal matrix. Generally, ametal matrix composite will show an improvement in such properties asstrength, stiffness, contact wear resistance, coefficient of thermalexpansion (C.T.E.), density, thermal conductivity and elevatedtemperature strength retention relative to the matrix metal inmonolithic form, but the degree to which any given property may beimproved depends largely on the specific constituents, their volume orweight fraction, and how they are processed in forming the composite. Insome instances, the composite also may be lighter in weight than thematrix metal per se. Aluminum matrix composites reinforced with ceramicssuch as silicon carbide in particulate, platelet, or whisker form, forexample, are of interest because of their higher specific stiffness(e.g., elastic modulus over density), wear resistance, thermalconductivity, low coefficient of thermal expansion (C.T.E.) and hightemperature strength and/or specific strength (e.g., strength overdensity) relative to aluminum.

Various metallurgical processes have been described for the fabricationof aluminum matrix composites, including methods based on powdermetallurgy techniques and liquid-metal infiltration techniques whichmake use of pressure casting, vacuum casting, stirring, and wettingagents. With powder metallurgy techniques, the metal in the form of apowder and the reinforcing material in the form of a powder, whiskers,chopped fibers, etc., are admixed and then either cold-pressed andsintered, or hot-pressed. The maximum ceramic volume fraction in siliconcarbide reinforced aluminum matrix composites produced by this methodhas been reported to be about 25 volume percent in the case of whiskers,and about 40 volume percent in the case of particulates.

The production of metal matrix composites by powder metallurgytechniques utilizing conventional processes imposes certain limitationswith respect to the characteristics of the products attainable. Thevolume fraction of the ceramic phase in the composite is limitedtypically, in the case of particulates, to about 40 percent. Also, thepressing operation poses a limit on the practical size attainable. Onlyrelatively simple product shapes are possible without subsequentprocessing (e.g., forming or machining) or without resorting to complexpresses. Also, nonuniform shrinkage during sintering can occur, as wellas nonuniformity of microstructure due to segregation in the compactsand grain growth.

U.S. Pat. No. 3,970,136, granted Jul. 20, 1976, to J. C. Cannell et al.,describes a process for forming a metal matrix composite incorporating afibrous reinforcement, e.g. silicon carbide or alumina whiskers, havinga predetermined pattern of fiber orientation. The composite is made byplacing parallel mats or felts of coplanar fibers in a mold with areservoir of molten matrix metal, e.g., aluminum, between at least someof the mats, and applying pressure to force molten metal to penetratethe mats and surround the oriented fibers. Molten metal may be pouredonto the stack of mats while being forced under pressure to flow betweenthe mats. Loadings of up to about 50% by volume of reinforcing fibers inthe composite have been reported.

The above-described infiltration process, in view of its dependence onoutside pressure to force the molten matrix metal through the stack offibrous mats, is subject to the vagaries of pressure-induced flowprocesses, i.e., possible non-uniformity of matrix formation, porosity,etc. Non-uniformity of properties is possible even though molten metalmay be introduced at a multiplicity of sites within the fibrous array.Consequently, complicated mat/reservoir arrays and flow pathways need tobe provided to achieve adequate and uniform penetration of the stack offiber mats. Also, the aforesaid pressure-infiltration method allows foronly a relatively low reinforcement to matrix volume fraction to beachieved because of the difficulty inherent in infiltrating a large matvolume. Still further, molds are required to contain the molten metalunder pressure, which adds to the expense of the process. Finally, theaforesaid process, limited to infiltrating aligned particles or fibers,is not directed to formation of aluminum metal matrix compositesreinforced with materials in the form of randomly oriented particles,whiskers or fibers.

In the fabrication of aluminum matrix-alumina filled composites,aluminum does not readily wet alumina, thereby making it difficult toform a coherent product. Various solutions to this problem have beensuggested. One such approach is to coat the alumina with a metal (e.g.,nickel or tungsten), which is then hot-pressed along with the aluminum.In another technique, the aluminum is alloyed with lithium, and thealumina may be coated with silica. However, these composites exhibitvariations in properties, or the coatings can degrade the filler, or thematrix contains lithium which can affect the matrix properties.

U.S. Pat. No. 4,232,091 to R. W. Grimshaw et al., overcomes certaindifficulties in the art which are encountered in the production ofaluminum matrix-alumina composites. This patent describes applyingpressures of 75-375 kg/cm² to force molten aluminum (or molten aluminumalloy) into a fibrous or whisker mat of alumina which has been preheatedto 700° to 1050° C. The maximum volume ratio of alumina to metal in theresulting solid casting was 0.25/1. Because of its dependency on outsideforce to accomplish infiltration, this process is subject to many of thesame deficiencies as that of Cannell et el.

European Patent Application Publication No. 115,742 describes makingaluminum-alumina composites, especially useful as electrolytic cellcomponents, by filling the voids of a preformed alumina matrix withmolten aluminum. The application emphasizes the non-wettability ofalumina by aluminum, and therefore various techniques are employed towet the alumina throughout the preform. For example, the alumina iscoated with a wetting agent of a diboride of titanium, zirconium,hafnium, or niobium, or with a metal, i.e., lithium, magnesium, calcium.titanium, chromium, iron, cobalt, nickel, zirconium, or hafnium. Inertatmospheres, such as argon, are employed to facilitate wetting. Thisreference also shows applying pressure to cause molten aluminum topenetrate an uncoated matrix. In this aspect, infiltration isaccomplished by evacuating the pores and then applying pressure to themolten aluminum in an inert atmosphere, e.g., argon. Alternatively, thepreform cab be infiltrated by vapor-phase aluminum deposition to wet thesurface prior to filling the voids by infiltration with molten aluminum.To assure retention of the aluminum in the pores of the preform, heattreatment, e.g., at 1400° to 1800° C., in either a vacuum or in argon isrequired. Otherwise, either exposure of the pressure infiltratedmaterial to gas or removal of the infiltration pressure will cause lossof aluminum from the body.

The use of wetting agents to effect infiltration of an alumina componentin an electrolytic cell with molten metal is also shown in EuropeanPatent Application Publication No. 94353. This publication describesproduction of aluminum by electrowinning with a cell having a cathodiccurrent feeder as a cell liner or substrate. In order to protect thissubstrate from molten cryolite, a thin coating of a mixture of a wettingagent and solubility suppressor is applied to the alumina substrateprior to start-up of the cell or while immersed in the molten aluminumproduced by the electrolytic process. Wetting agents disclosed aretitanium, zirconium, hafnium, silicon, magnesium, vanadium, chromium,niobium, or calcium, and titanium is stated as the preferred agent.Compounds of boron, carbon and nitrogen are described as being useful insuppressing the solubility of the wetting agents in molten aluminum. Thereference, however, does not suggest the production of metal matrixcomposites, nor does it suggest the formation of such a composite in,for example, a nitrogen atmosphere.

In addition to application of pressure and wetting agents, it has beendisclosed that an applied vacuum will aid the penetration of moltenaluminum into a porous ceramic compact. For example, U.S. Pat. No.3,718,441, granted Feb. 27, 1973, to R. L. Landingham, reportsinfiltration of a ceramic compact (e.g., boron carbide, alumina andberyllia) with either molten aluminum, beryllium, magnesium, titanium,vanadium, nickel or chromium under a vacuum of less than 10⁻⁶ torr. Avacuum of 10⁻² to 10⁻⁶ tort resulted in poor wetting of the ceramic bythe molten metal to the extent that the metal did not flow freely intothe ceramic void spaces. However, wetting was said to have improved whenthe vacuum was reduced to less than 10⁻⁶ tort.

U.S. Pat. No. 3,864,154, granted Feb. 4, 1975, to G. E. Gazza et al.,also shows the use of vacuum to achieve infiltration. This patentdescribes loading a cold-pressed compact of AlB₁₂ powder onto a bed ofcold-pressed aluminum powder. Additional aluminum was then positioned ontop of the AlB₁₂ powder compact. The crucible, loaded with the AlB₁₂compact "sandwiched" between the layers of aluminum powder, was placedin a vacuum furnace. The furnace was evacuated to approximately 10⁻⁵torr to permit outgassing. The temperature was subsequently raised to1100° C. and maintained for a period of 3 hours. At these conditions,the molten aluminum penetrated the porous AlB₁₂ compact.

U.S. Pat. No. 3,364,976, granted Jan. 23, 1968 to John N. Reding et al.,discloses the concept of creating a self-generated vacuum in a body toenhance penetration of a molten metal into the body. Specifically, it isdisclosed that a body, e.g., a graphite mold, a steel mold, or a porousrefractory material, is entirely submerged in a molten metal. In thecase of a mold, the mold cavity, which .is filled with a gas reactivewith the metal, communicates with the externally located molten metalthrough at least one orifice in the mold. When the mold is immersed intothe melt, filling of the cavity occurs as the self-generated vacuum isproduced from the reaction between the gas in the cavity and the moltenmetal. Particularly, the vacuum is a result of the formation of a solidoxidized form of the metal. Thus, Reding et al. disclose that it isessential to induce a reaction between gas in the cavity and the moltenmetal. However, utilizing a mold to create a vacuum may be undesirablebecause of the inherent limitations associated with use of a mold. Moldsmust first be machined into a particular shape; then finished, machinedto produce an acceptable casting surface on the mold; then assembledprior to their use; then disassembled after their use to remove the castpiece therefrom; and thereafter reclaim the mold, which most likelywould include refinishing surfaces of the mold or discarding the mold ifit is no longer acceptable for use. Machining of a mold into a complexshape can be very costly and time-consuming. Moreover, removal of aformed piece from a complex-shaped mold can also be difficult (i.e.,cast pieces having a complex shape could be broken when removed from themold). Still further, while there is a suggestion that a porousrefractory material can be immersed directly in a molten metal withoutthe need for a mold, the refractory material would have to be anintegral piece because there is no provision for infiltrating a loose orseparated porous material absent the use of a container mold (i.e., itis generally believed that the particulate material would typicallydisassociate or float apart when placed in a molten metal). Stillfurther, if it was desired to infiltrate a particulate material orloosely formed preform, precautions should be taken so that theinfiltrating metal does not displace at least portions of theparticulate or preform resulting in a non-homogeneous microstructure.

Accordingly, there has been a long felt need for a simple and reliableprocess to produce shaped metal matrix composites which does not relyupon the use of applied pressure or vacuum (whether externally appliedor internally created), or damaging wetting agents to create a metalmatrix embedding another material such as a ceramic material. Moreover,there has been a long felt need to minimize the amount of finalmachining operations needed to produce a metal matrix composite body.The present invention satisfies these needs by providing, in a preferredembodiment, a spontaneous infiltration mechanism for infiltrating arigidized mass of filler material (e.g., a ceramic material) or arigidized preform of filler material with molten matrix metal (e.g.,aluminum) in the presence of an infiltrating atmosphere (e.g., nitrogen)under normal atmospheric pressures so long as an infiltration enhancerprecursor and/or infiltration enhancer is present at least at some pointduring the process.

DESCRIPTION OF COMMONLY OWNED U.S. PATENT APPLICATIONS

The present invention is a Continuation-in-Part of U.S. patentapplication Ser. No. 07/521,200, filed May 9, 1990, in the names ofRocazella et al. and entitled "A Method for Forming Metal MatrixComposite Bodies by Rigidizing a Filler Material and Articles ProducedTherefrom".

The subject matter of this application is further related to that ofseveral other copending and co-owned patent applications and issuedPatents. Particularly, these other copending patent applications andissued Patents describe novel methods for making metal matrix compositematerials (hereinafter sometimes referred to as "Commonly Owned MetalMatrix Patents and Patent Applications").

A novel method of making a metal matrix composite material is disclosedin Commonly Owned U.S. patent application Ser. No. 049,171, filed May13, 1987, in the names of White et al., and entitled "Metal MatrixComposites", now U.S. Pat. No. 4,828,008, which issued on May 9, 1989,and which published in the EPO on Nov. 17, 1988, as Publication No.0291441. According to the method of this White et invention, a metalmatrix composite is produced by infiltrating a permeable mass of fillermaterial (e.g., a ceramic or a ceramic-coated material) with moltenaluminum containing at least about 1 percent by weight magnesium, andpreferably at least about 3 percent by weight magnesium. Infiltrationoccurs spontaneously without the application of external pressure orvacuum. A supply of the molten metal alloy is contacted with the mass offiller material at a temperature of at least about 675° C. in thepresence of a gas comprising from about 10 to 100 percent, andpreferably at least about 50 percent, nitrogen by volume, and aremainder of the gas, if any, being a nonoxidizing gas, e.g., argon.Under these conditions, the molten aluminum alloy infiltrates theceramic mass under normal atmospheric pressures to form an aluminum (oraluminum alloy) matrix composite. When the desired amount of fillermaterial has been infiltrated with the molten aluminum alloy, thetemperature is lowered to solidify the alloy, thereby forming a solidmetal matrix structure that embeds the reinforcing filler material.Usually, and preferably, the supply of molten alloy delivered will besufficient to permit the infiltration to proceed essentially to theboundaries of the mass of filler material. The amount of filler materialin the aluminum matrix composites produced according to the White et al.invention may be exceedingly high. In this respect, filler to alloyvolumetric ratios of greater than 1:1 may be achieved.

Under the process conditions in the aforesaid White et al. invention,aluminum nitride can form as a discontinuous phase dispersed throughoutthe aluminum matrix. The amount of nitride in the aluminum matrix mayvary depending on such factors as temperature, alloy composition, gascomposition and filler material. Thus, by controlling one or more suchfactors in the system, it is possible to tailor certain properties ofthe composite. For some end use applications, however, it may bedesirable that the composite contain little or substantially no aluminumnitride.

It has been observed that higher temperatures favor infiltration butrender the process more conducive to nitride formation. The White et al.invention allows the choice of a balance between infiltration kineticsand nitride formation.

An example of suitable barrier means for use with metal matrix compositeformation is described in Commonly Owned U.S. Pat. No. 4,935,055, whichissued on Jun. 19, 1990, from U.S. patent application Ser. No.07/141,642, filed Jan. 7, 1988, in the names of Michael K. Aghajanian etal., and entitled "Method of Making Metal Matrix Composite with the Useof a Barrier" (now allowed in the United States), and which published inthe EPO on Jul. 12, 1989, as Publication No. 0323945. According to themethod of this Aghajanian et al. invention, a barrier means (e.g.,particulate titanium diboride or a graphite material such as a flexiblegraphite foil product sold by Union Carbide under the trade nameGRAFOIL®) is disposed on a defined surface boundary of a filler materialand matrix alloy infiltrates up to the boundary defined by the barriermeans. The barrier means is used to inhibit, prevent, or terminateinfiltration of the molten alloy, thereby providing net, or near net,shapes in the resultant metal matrix composite. Accordingly, the formedmetal matrix composite bodies have an outer shape which substantiallycorresponds to the inner shape of the barrier means.

The method of U.S. Pat. No. 4,828,008 was improved upon by CommonlyOwned and Copending U.S. patent application Ser. No. 07/517,541, filedApr. 24, 1990, which is a Continuation of U.S. patent application Ser.No. 07/168,284, filed Mar. 15, 1988, in the names of Michael K.Aghajanian and Marc S. Newkirk and entitled "Metal Matrix Composites andTechniques for Making the Same", and which published in the EPO on Sep.20, 1989, as Publication No. 0333629. In accordance with the methodsdisclosed in these U.S. patent applications, a matrix metal alloy ispresent as a first source of metal and as a reservoir of matrix metalalloy which communicates with the first source of molten metal due to,for example, gravity flow. Particularly, under the conditions describedin this patent application, the first source of molten matrix alloybegins to infiltrate the mass of filler material under normalatmospheric pressures and thus begins the formation of a metal matrixcomposite. The first source of molten matrix metal alloy is consumedduring its infiltration into the mass of filler material and, ifdesired, can be replenished, preferably by a continuous means, from thereservoir of molten matrix metal as the spontaneous infiltrationcontinues. When a desired amount of permeable filler has beenspontaneously infiltrated by the molten matrix alloy, the temperature islowered to solidify the alloy, thereby forming a solid metal matrixstructure that embeds the reinforcing filler material. It should beunderstood that the use of a reservoir of metal is simply one embodimentof the invention described in this patent application and it is notnecessary to combine the reservoir embodiment with each of the alternateembodiments of the invention disclosed therein, some of which could alsobe beneficial to use in combination with the present invention.

The reservoir of metal can be present in an amount such that it providesfor a sufficient amount of metal to infiltrate the permeable mass offiller material to a predetermined extent. Alternatively, an optionalbarrier means can contact the permeable mass of filler on at least oneside thereof to define a surface boundary.

Moreover, while the supply of molten matrix alloy delivered should be atleast sufficient to permit spontaneous infiltration to proceedessentially to the boundaries (e.g., barriers) of the permeable mass offiller material, the amount of alloy present in the reservoir couldexceed such sufficient amount so that not only will there be asufficient amount of alloy for complete infiltration, but excess moltenmetal alloy could remain and be attached to the metal matrix compositebody. Thus, when excess molten alloy is present, the resulting body willbe a complex composite body (e.g., a macrocomposite), wherein aninfiltrated ceramic body having a metal matrix therein will be directlybonded to excess metal remaining in the reservoir.

Further improvements in metal matrix technology can be found in commonlyowned and copending U.S. patent application Ser. No. 7/521,043, filedMay 9, 1990, which is a Continuation-in-Part application of U.S. patentapplication Ser. No. 07/484,753, filed Feb. 23, 1990, which is aContinuation-in-Part application of U.S. patent application Ser. No.07/432,661, filed Nov. 7, 1989, which is a Continuation-in-Partapplication of U.S. patent application Ser. No. 07/416,327, filed Oct.6, 1989 (now abandoned), which is a continuation-in-part application ofU.S. patent application Ser. No. 7/349,590, filed May 9, 1989 (nowabandoned), which in turn is a continuation-in-part application of U.S.patent application Ser. No. 7/269,311, filed Nov. 10, 1988 (nowabandoned), all of which were filed in the names of Michael K.Aghajanian et al. and all of which are entitled "A Method of FormingMetal Matrix Composite Bodies By A Spontaneous Infiltration Process, andProducts Produced Therefrom" (an EPO application corresponding to U.S.patent application Ser. No. 7/416,327 was published in the EPO on Jun.27, 1990, as European Publication No. 0375588). According to theseAghajanian et al. applications, spontaneous infiltration of a matrixmetal into a permeable mass of filler material or preform is achieved byuse of an infiltration enhancer and/or an infiltration enhancerprecursor and/or an infiltrating atmosphere which are in communicationwith the filler material or preform, at least at some point during theprocess, which permits molten matrix metal to spontaneously infiltratethe filler material of preform. Aghajanian et el. disclose a number ofmatrix metal/infiltration enhancer precursor/infiltrating atmospheresystems which exhibit spontaneous infiltration. Specifically, Aghajanianet al. disclose that spontaneous infiltration behavior has been observedin the aluminum/magnesium/nitrogen system; thealuminum/strontium/nitrogen system; the aluminum/zinc/oxygen system; andthe aluminum/calcium/nitrogen system. However, it is clear from thedisclosure set forth in the Aghajanian et al. applications that thespontaneous infiltration behavior should occur in other matrixmetal/infiltration enhancer precursor/infiltrating atmosphere systems.

Each of the above-discussed Commonly Owned Metal Matrix Patents andPatent Applications describes methods for the production of metal matrixcomposite bodies and novel metal matrix composite bodies which areproduced therefrom. The entire disclosures of all of the foregoingCommonly Owned Metal Matrix Patents and Patent Applications areexpressly incorporated herein by reference.

SUMMARY OF THE INVENTION

A metal matrix composite body is produced by infiltrating a rigidizedpermeable mass of filler material or a rigidized preform with a moltenmatrix metal. Specifically, in a particularly preferred embodiment forforming metal matrix composites by a spontaneous infiltration technique,an infiltration enhancer and/or an infiltration enhancer precursorand/or an infiltrating atmosphere are in communication with therigidized filler material or preform, at least at some point during theprocess, which permits molten matrix metal to spontaneously infiltratethe rigidized filler material or preform.

It has been discovered that, in some cases, spontaneous infiltration ofa molten matrix metal into a filler material or preform may result inminor microstructural modifications of the filler material or preform.Specifically, the formation of infiltration enhancer from aninfiltration enhancer precursor may result in an overall volumetricexpansion which could cause a minor displacement of filler material whenthe filler material is tightly packed. For example, if infiltrationenhancer was formed as a coating on a filler material or preform and thefiller material or preform was relatively dense, the formation of acoating could result in a minor displacement of filler materialresulting in the formation of minor cracks in the filler material orpreform and/or a lower volume percent of filler in the resultant metalmatrix composite body. The formed minor cracks could lead to metal richchannels in the metal matrix composite body which, for someapplications, may not be desirable. The actual infiltration of a matrixmetal into a preform or filler material may result in a similar minormovement of a filler material or preform with the same attendantdisadvantages. The present invention provides a means for assuring thatdisplacement of a loose filler or a preform of filler material isminimized as well as maximizing the volume percent of filler material,thus enhancing the resultant properties of a formed metal matrixcomposite body.

Moreover, although the present invention discusses primarily theformation of metal matrix composite bodies by a spontaneous infiltrationprocess, it should be understood by those having ordinary skill in theart that the present invention is applicable to any metal matrixcomposite formation technique (e.g., pressure infiltration, vacuuminfiltration, etc.) wherein the use of a rigidized filler or rigidizedpreform may enhance the resultant properties of a formed metal matrixcomposite body.

In a first preferred embodiment, a rigidized filler material or preformis achieved by mixing a filler material with a colloidal oxide binder(e.g., colloidal alumina, colloidal silica, etc.). The colloidal oxidebinder causes the formation of a three-dimensionally interconnectedmatrix within the filler material which functions as a rigidizingskeleton for the filler material when, for example, the colloidal oxideand the filler material or preform are heated to a sufficienttemperature for a sufficient time to result in an at least partiallythree-dimensional permeable mass. The skeleton that is formed maycomprise a mixture of both colloidal oxide and filler material. Theamount of colloidal oxide required to obtain desirable rigidizingproperties can vary from about 1 weight percent to about 15 weightpercent. The colloidal oxide may also affect the resultant properties ofa formed metal matrix composite body. Specifically, typically, thecolloidal oxide will be embedded by the matrix metal, thereby serving asa filler material.

In a second preferred embodiment of the invention, a filler material orpreform can be rigidized by firing (e.g., at least partially sinteringthe filler material or preform) so as to provide a three-dimensionallyinterconnected network of filler material. A sintering aid may or maynot be required. The extent of firing (e.g., time and temperature)depends upon the amount of porosity desired in the filler material orpreform prior to infiltration occurring. By increasing the density ofthe filler material or preform, the resultant volume percent of fillermaterial present in the formed metal matrix composite increases. Forexample, by firing a silicon carbide filler material or preform in anoxygen-containing atmosphere, at least some of the silicon carbide mayreact with the oxygen to form silica, thereby increasing the volume offiller material to be infiltrated by the matrix metal. However, firingshould not result in the complete closure of all interconnected porositybecause spontaneous infiltration of molten matrix metal into the fillermaterial would be adversely affected (e.g., if the interconnectedporosity was eliminated, the matrix metal would have no means toinfiltrate and embed the filler material).

In a third preferred embodiment, a supportive structural refractorymaterial (e.g., including, but not limited to, materials such as steel,graphite, glass frit, colloidal oxide, etc.) surrounds at least asubstantial portion of a filler material or preform and providesexternal structural support. Specifically, a filler material or preformmay be placed within a rigid structure so as to prevent the fillermaterial or preform from deforming during any portion of the spontaneousinfiltration process. Alternatively, a precursor to a supportivestructural refractory material could be provided to an exterior surface(e.g., coated upon an exterior surface) of a preform or filler materialand become structurally supportive prior to molten matrix metalcontacting said filler material or preform. The physical containerand/or the refractory material surrounding a preform or filler materialcan be of any desirable composition and/or thickness with the primaryselection criteria being that the material does not adversely affectspontaneous infiltration and that the material functions as a rigidizingmeans.

In a fourth preferred embodiment of the invention, each of the threeaforementioned embodiments may be combined, in any manner, so as toenhance synergistically the rigidizing effects of each. For example, acolloidal oxide may be mixed with a filler material in combination withthe placement of an exterior rigidizing means. Such combination mayenhance further the rigidizing effects on a filler material or preform.

In a final preferred embodiment of the invention, when an infiltrationenhancer precursor is caused to volatilize and react with, for example,an infiltrating atmosphere to form infiltration enhancer in at least aportion of a filler material or preform, the amount of infiltrationenhancer that is formed can be minimized so as to reduce any deleteriouseffects that such formation may have. Particularly, for example, in thealuminum/magnesium/nitrogen system, when magnesium volatilizes andreacts with nitrogen, a magnesium nitride infiltration enhancer isformed in at least a portion of the preform or filler material. Theformation of magnesium nitride, in excessive amounts, could result in avolumetric expansion of the preform or filler material. Such volumetricexpansion could lead to microcracks within a preform or filler material.Accordingly, by controlling time and/or temperature and/or the amount ofinfiltration enhancer precursor and/or amount of infiltratingatmosphere, etc., the amount of infiltration enhancer which is formed ina preform or filler material can be controlled so that just a sufficientamount is manufactured to achieve desirable spontaneous infiltration.

In each of the above-discussed preferred embodiments, a precursor to aninfiltration enhancer may be supplied to at least one of a fillermaterial or preform, and/or a matrix metal and/or an infiltratingatmosphere. The supplied infiltration enhancer precursor may thereafterreact with at least one of the filler material or preform and/or thematrix metal and/or the infiltrating atmosphere to produce infiltrationenhancer in at least a portion of, or on, the filler material orpreform. Ultimately, at least during the spontaneous infiltration, adesirable amount of infiltration enhancer should be in contact with atleast a portion of the filler material or preform.

In another preferred embodiment of the invention, rather than supplyingan infiltration enhancer precursor, an infiltration enhancer may besupplied directly to at least one of the preform, and/or matrix metal,and/or infiltrating atmosphere. Ultimately, at least during thespontaneous infiltration, the infiltration enhancer should be in contactwith at least a portion of the filler material or preform.

This application discusses various examples of matrix metals, which atsome point during the formation of a metal matrix composite contactedwith an infiltration enhancer precursor, in the presence of aninfiltrating atmosphere. Thus, various references will be made toparticular matrix metal/infiltration enhancer precursor/infiltratingatmosphere systems which exhibit spontaneous infiltration. However, itis conceivable that many other matrix metal/infiltration enhancerprecursor/infiltrating atmosphere systems other than those discussed inthis application may behave in a manner similar to the systems discussabove herein. Specifically, spontaneous infiltration behavior has beenobserved in the aluminum/magnesium/nitrogen system; thealuminum/strontium/nitrogen system; the aluminum/zinc/oxygen system; andthe aluminum/calcium/nitrogen system. Accordingly, even though thisapplication discusses only those systems referred to above herein (withparticular emphasis being placed upon the aluminum/magnesium/nitrogensystem), it should be understood that other matrix metal/infiltrationenhancer precursor/infiltrating atmosphere systems may behave in asimilar manner.

In a preferred embodiment for achieving spontaneous infiltration into apermeable mass of filler material or a preform, molten matrix metal iscontacted with the preform or filler material. The preform or fillermaterial may have admixed therewith, and/or at some point during theprocess, be exposed to, an infiltration enhancer precursor. Moreover, ina preferred embodiment, the molten matrix metal and/or preform or fillermaterial communicate with an infiltrating atmosphere for at least aportion of the process. In another preferred embodiment, the matrixmetal and/or preform or filler material communicate with an infiltratingatmosphere for substantially all of the process. The preform or fillermaterial will be spontaneously infiltrated by molten matrix metal, andthe extent or rate of spontaneous infiltration and formation of metalmatrix composite will vary with a given set of processing conditionsincluding, for example, the concentration of infiltration enhancerprecursor provided to the system (e.g., in the molten matrix alloyand/or in the filler material or preform and/or in the infiltratingatmosphere), the size and/or composition of the filler material, thesize and/or composition of particles in the preform, the availableporosity for infiltration into the preform or filler material, the timepermitted for infiltration to occur, and/or the temperature at whichinfiltration occurs. Spontaneous infiltration typically occurs to anextent sufficient to embed substantially completely the preform orfiller material.

Moreover, by varying the composition of the matrix metal and/or theprocessing conditions, the physical and mechanical properties of theformed metal matrix composite bodies may be engineered to any particularapplication or need. Further, by subjecting a formed metal matrixcomposite body to a post treatment process (e.g., directionalsolidification, heat treatment, etc.) the mechanical and/or physicalproperties may be further engineered to meet any particular applicationor need. Still further, by controlling the processing conditions duringthe formation of a metal matrix composite the nitrogen content of theformed metal matrix composite may be tailored to meet a wide range ofindustrial applications.

Moreover, by controlling the composition and/or size (e.g., particlediameter) and/or geometry of the filler material or the materialcomprising the preform, the physical and/or mechanical properties of theformed metal matrix composite can be controlled or engineered to meetany number of industrial needs. For example, it has been discovered thatwear resistance of the metal matrix composite can be increased byincreasing the size of the filler material (e.g., increasing the averagediameter of the filler material particles), given that the wearresistance of filler material is higher than that of the matrix metal.However, strength and/or toughness may tend to increase with decreasingfiller size. Further, the thermal expansion coefficient of the metalmatrix composite may decrease with increasing filler loading, given thatthe coefficient of thermal expansion of the filler is lower than thecoefficient of thermal expansion of the matrix metal. Still further, themechanical and/or physical properties (e.g., density, elastic and/orspecific modulus, strength and/or specific strength, etc.) of a formedmetal matrix composite body may be tailored depending on the loading ofthe filler material in the loose mass or in the preform. For example, byproviding a loose mass or preform comprising a mixture of fillerparticles of varying sizes and/or shapes, wherein the density of thefiller is greater than that of the matrix metal, a higher fillerloading, due to enhanced packing of the filler material, may beachieved, thereby resulting in a metal matrix composite body with anincreased density. Moreover, by following the teachings of the presentinvention, even higher filler loadings can be achieved by minimizing theability of the preform or filler material to be displaced or movedduring any portion of the spontaneous infiltration process. By utilizingthe teachings of the present invention, the volume percent of fillermaterial or preform which can be infiltrated can vary over a wide range.The lower volume percent of filler that can be infiltrated is limitedprimarily by the ability to form a porous filler material or preform,(e.g., about 10 volume percent); whereas the higher volume percent offiller or preform that can be infiltrated is limited primarily by theability to form a dense and rigid filler material or preform (e.g.,about 95 volume percent) with at least some interconnected porosity.Accordingly, by practicing any of the above teachings, alone or incombination, a metal matrix composite can be engineered to contain adesired combination of properties.

DEFINITIONS

"Aluminum", as used herein, means and includes essentially pure metal(e.g., a relatively pure, commercially available unalloyed aluminum) orother grades of metal and metal alloys such as the commerciallyavailable metals having impurities and/or alloying constituents such asiron, silicon, copper, magnesium, manganese, chromium, zinc, etc.,therein. An aluminum alloy for purposes of this definition is an alloyor intermetallic compound in which aluminum is the major constituent.

"Balance Non-Oxidizing Gas", as used herein, means that any gas presentin addition to the primary gas comprising the infiltrating atmosphere,is either an inert gas or a reducing gas which is substantiallynon-reactive with the matrix metal under the process conditions. Anyoxidizing gas which may be present as an impurity in the gas(es) usedshould be insufficient to oxidize the matrix metal to any substantialextent under the process conditions.

"Barrier" or "barrier means", as used herein, means any suitable meanswhich interferes with, inhibits, prevents or terminates the migration,movement, or the like, of molten matrix metal beyond a surface boundaryof a permeable mass of filler material or preform, where such surfaceboundary is defined by said barrier means. Suitable barrier means may beany such material, compound, element, composition, or the like, which,under the process conditions, maintains some integrity and is notsubstantially volatile (i.e., the barrier material does not volatilizeto such an extent that it is rendered non-functional as a barrier).

Further, suitable "barrier means" include materials which aresubstantially non-wettable by the migrating molten matrix metal underthe process conditions employed. A barrier of this type appears toexhibit substantially little or no affinity for the molten matrix metal,and movement beyond the defined surface boundary of the mass of fillermaterial or preform is prevented or inhibited by the barrier means. Thebarrier reduces any final machining or grinding that may be required anddefines at least a portion of the surface of the resulting metal matrixcomposite product. The barrier may in certain cases be permeable orporous, or rendered permeable by, for example, drilling holes orpuncturing the barrier, to permit gas to contact the molten matrixmetal, etc.

"Carcass" or "CarCass of Matrix Metal", as used herein, refers to any ofthe original body of matrix metal remaining which has not been consumedduring formation of the metal matrix composite body, and typically, ifallowed to cool, remains in at least partial contact with the metalmatrix composite body which has been formed. It should be understoodthat the carcass may also include a second or foreign metal therein.

"Filler", as used herein, is intended to include either singleconstituents or mixtures of constituents which are substantiallynonreactive with and/or of limited solubility in the matrix metal andmay be single or multi-phase. Fillers may be provided in a wide varietyof forms and sizes, such as powders, flakes, platelets, microspheres,whiskers, bubbles, fibers, particulates, fiber mats, chopped fibers,spheres, pellets, tubules, refractory cloths, etc., and may be eitherdense or porous. "Filler" may also include ceramic fillers, such asalumina or silicon carbide as fibers, chopped fibers, particulates,whiskers, bubbles, spheres, fiber mats, or the like, and ceramic-coatedfillers such as carbon fibers coated with alumina or silicon carbide toprotect the carbon from attack, for example, by a molten aluminum matrixmetal. Fillers may also include metals.

"Hot-Topping", as used herein, refers to the placement of a substance onone end (the "topping" end) of an at least partially formed metal matrixcomposite which reacts exothermically with at least one of the matrixmetal and/or filler material and/or with another material supplied tothe topping end. This exothermic reaction should provide sufficient heatto maintain the matrix metal at the topping end in a molten state whilethe balance of the matrix metal in the composite cools to solidificationtemperature.

"Infiltrating Atmosphere", as used herein, means that atmosphere whichis present which interacts with the matrix metal and/or preform (orfiller material) and/or infiltration enhancer precursor and/orinfiltration enhancer and permits or enhances spontaneous infiltrationof the matrix metal.

"Infiltration Enhancer", as used herein, means a material which promotesor assists in the spontaneous infiltration of a matrix metal into afiller material or preform. An infiltration enhancer may be formed from,for example, (1) a reaction of an infiltration enhancer precursor withan infiltrating atmosphere to form a gaseous species and/or (2) areaction product of the infiltration enhancer precursor and theinfiltrating atmosphere and/or (3) a reaction product of theinfiltration enhancer precursor and the filler material or preform.Moreover, the infiltration enhancer may be supplied directly to at leastone of the preform, and/or matrix metal, and/or infiltrating atmosphereand function in a substantially similar manner to an infiltrationenhancer which has formed from a reaction between an infiltrationenhancer precursor and another species. Ultimately, at least during thespontaneous infiltration, the infiltration enhancer should be located inat least a portion of the filler material or preform to achievespontaneous infiltration, and the infiltration enhancer may be at leastpartially reducible by the matrix metal.

"Infiltration Enhancer Precursor" or "Precursor to the InfiltrationEnhancer", as used herein, means a material which when used incombination with (1) the matrix metal, (2) the preform or fillermaterial and/or (3) an infiltrating atmosphere forms an infiltrationenhancer which induces or assists the matrix metal to spontaneouslyinfiltrate the filler material or preform. Without wishing to be boundby any particular theory or explanation, it appears as though it may benecessary for the precursor to the infiltration enhancer to be capableof being positioned, located or transportable to a location whichpermits the infiltration enhancer precursor to interact with theinfiltrating atmosphere and/or the preform or filler material and/or thematrix metal. For example, in some matrix metal/infiltration enhancerprecursor/infiltrating atmosphere systems, it is desirable for theinfiltration enhancer precursor to volatilize at, near, or in somecases, even somewhat above the temperature at which the matrix metalbecomes molten. Such volatilization may lead to: (1) a reaction of theinfiltration enhancer precursor with the infiltrating atmosphere to forma gaseous species which enhances wetting of the filler material orpreform by the matrix metal; and/or (2) a reaction of the infiltrationenhancer precursor with the infiltrating atmosphere to form a solid,liquid or gaseous infiltration enhancer in at least a portion of thefiller material or preform which enhances wetting; and/or (3) a reactionof the infiltration enhancer precursor within the filler material orpreform which forms a solid, liquid or gaseous infiltration enhancer inat least a portion of the filler material or preform which enhanceswetting.

"Matrix Metal" or "Matrix Metal Alloy", as used herein, means that metalwhich is utilized to form a metal matrix composite body (e.g., beforeinfiltration) and/or that metal which is intermingled with a fillermaterial to form a metal matrix composite body (e.g., afterinfiltration). When a specified metal is mentioned as the matrix metal,it should be understood that such matrix metal includes that metal as anessentially pure metal, a commercially available metal having impuritiesand/or alloying constituents therein, an intermetallic compound or analloy in which that metal is the major or predominant constituent.

"Matrix Metal/Infiltration Enhancer Precursor/Infiltrating AtmosphereSystem" or "Spontaneous System", as used herein, refers to thatcombination of materials which exhibit spontaneous infiltration into apreform or filler material. It should be understood that whenever a "/"appears between an exemplary matrix metal, infiltration enhancerprecursor and infiltrating atmosphere that the "/" is used to designatea system or combination of materials which, when combined in aparticular manner, exhibits spontaneous infiltration into a preform orfiller material.

"Metal Matrix Composite" or "MMC", as used herein, means a materialcomprising a two- or three-dimensionally interconnected alloy or matrixmetal which has embedded a preform or filler material. The matrix metalmay include various alloying elements to provide specifically desiredmechanical and physical properties in the resulting composite.

A Metal "Different" from the Matrix Metal means a metal which does notcontain, as a primary constituent, the same metal as the matrix metal(e.g., if the primary constituent of the matrix metal is aluminum, the"different" metal could have a primary constituent of, for example,nickel).

"Nonreactive Vessel for Housing Matrix Metal" means any vessel which canhouse or contain a filler material (or preform) and/or molten matrixmetal under the process conditions and not react with the matrix and/orthe infiltrating atmosphere and/or infiltration enhancer precursorand/or a filler material or preform in a manner which would besignificantly detrimental to the spontaneous infiltration mechanism. Thenonreactive vessel may be disposable and removable after the spontaneousinfiltration of the molten matrix metal has been completed.

"Preform" or "Permeable Preform", as used herein, means a porous mass offiller or filler material which is manufactured with at least onesurface boundary which essentially defines a boundary for infiltratingmatrix metal, such mass retaining sufficient shape integrity and greenstrength to provide dimensional fidelity prior to being infiltrated bythe matrix metal. The mass should be sufficiently porous to accommodatespontaneous infiltration of the matrix metal thereinto. A preformtypically comprises a bonded array or arrangement of filler, eitherhomogeneous or heterogeneous, and may be comprised of any suitablematerial (e.g., ceramic and/or metal particulates, powders, fibers,whiskers, etc., and any combination thereof). A preform may exist eithersingularly or as an assemblage.

"Reservoir", as used herein, means a separate body of matrix metalpositioned relative to a mass of filler or a preform so that, when themetal is molten, it may flow to replenish, or in some cases to initiallyprovide and subsequently replenish, that portion, segment or source ofmatrix metal which is in contact with the filler or preform.

"Rigidized", as used herein,.means that a preform or filler material hasbeen made stronger so as to be more resistive to relative displacementby any exerted stresses.

"Spontaneous Infiltration", as used herein, means the infiltration ofmatrix metal into the permeable mass of filler or preform occurs withoutrequirement for the application of pressure or vacuum (whetherexternally applied or internally created).

BRIEF DESCRIPTION OF DRAWINGS

The following Figures are provided to assist in understanding theinvention, but are not intended to limit the scope of the invention.Similar reference numerals have been used wherever possible in each ofthe Figures to denote like components, wherein:

FIG. 1 is a schematic cross-sectional view of a lay-up used inaccordance with Example 1 of the present invention;

FIG. 2 is a schematic cross-sectional view of a lay-up used inaccordance with Example 2 of the present invention;

FIG. 3 is a schematic cross-sectional view of a lay-up used inaccordance with Example 3 of the present invention;

FIG. 4 is a schematic cross-sectional view of a lay-up used inaccordance with Example 4 of the present invention;

FIG. 5 is a schematic cross-sectional view of a lay-up used inaccordance with Example 5 of the present invention;

FIG. 6 is a schematic cross-sectional view of a lay-up used inaccordance with Example 7 of the present invention;

FIG. 7 is a schematic cross-sectional view of a lay-up used inaccordance with Example 8, Sample A, of the present invention;

FIG. 8 is a schematic cross-sectional view of a lay-up used inaccordance with Example 9 of the present invention;

FIG. 9 is a schematic cross-sectional view of a lay-up used inaccordance with Example 10 of the present invention;

FIG. 10 is a schematic cross-sectional view of a lay-up used inaccordance with Example 11 of the present invention; and

FIG. 11 is a schematic cross-sectional view of a lay-Up used inaccordance with Example 12 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention relates to forming a metal matrix composite byinfiltrating a rigidized filler material or preform with molten matrixmetal. Specifically, in a particularly preferred method for formingmetal matrix composite bodies by a spontaneous infiltration technique,an infiltration enhancer and/or an infiltration enhancer precursorand/or an infiltrating atmosphere are in communication with therigidized filler material or preform, at least at some point during theprocess, which permits molten matrix metal to spontaneously infiltratethe rigidized filler material or preform.

In a first preferred embodiment, a rigidized filler material or preformis achieved by mixing a filler material with a colloidal oxide binder(e.g., colloidal alumina, colloidal silica, etc.). The colloidal oxidebinder causes the formation of a three-dimensionally interconnectedmatrix within the filler material which functions as a rigidizingskeleton for the filler material when, for example, the colloidal oxideand the filler material or preform are heated to a sufficienttemperature for a sufficient time to result in an at least partiallythree-dimensional permeable mass. The skeleton that is formed maycomprise a mixture of both colloidal oxide and filler material. Theamount of colloidal oxide required to obtain desirable rigidizingeffects can vary from about 1 weight percent to about 15 weight percent.The colloidal oxide may also affect the resultant properties of a formedmetal matrix composite body. Specifically, typically, the colloidaloxide will be embedded by the matrix metal, thereby serving as a fillermaterial.

In a second preferred embodiment of the invention, a filler material orpreform can be rigidized by firing (e.g., at least partially sinteringthe filler material) so as to provide a three-dimensionallyinterconnected network of filler material. A sintering aid may or maynot be required. The extent of firing (e.g., time and temperature)depends upon the amount of porosity desired in the filler material orpreform prior to infiltration occurring. By increasing the density ofthe filler material or preform, the resultant volume percent of fillermaterial present in the formed metal matrix composite increases. Forexample, by firing a silicon carbide filler material in the presence ofan oxygen-containing gas, at least some of the silicon carbide may reactwith the oxygen to form silica, thereby increasing the volume of fillerto be infiltrated by the matrix metal. However, firing should not resultin the complete closure of all interconnected porosity becauseinfiltration of molten matrix metal into the filler material would beadversely affected (e.g., if the interconnected porosity was eliminated,the matrix metal would have no means to infiltrate and embed the fillermaterial).

In a third preferred embodiment, a supportive structural refractorymaterial (e.g., including, but not limited to, materials such as steel,graphite, glass frit, colloidal oxide, etc.) surrounds at least asubstantial portion of a filler material or preform and providesexternal structural support. Specifically, a filler material or preformmay be placed within a rigid structure so as to prevent the fillermaterial or preform from deforming during any portion of theinfiltration process. Alternatively, a precursor to a supportivestructural refractory material could be provided to an exterior surface(e.g., coated upon an exterior surface) of a preform or filler materialand become structurally support lye prior to molten matrix metalcontacting said filler material or preform. The physical containerand/or the refractory material surrounding a preform or filler materialcan be of any desirable composition and/or thickness with the primaryselection criteria being that the material does not adversely affectinfiltrating and that the material functions as a rigidizing means.

In a fourth preferred embodiment of the invention, each of the threeaforementioned embodiments may be combined, in any manner, so as toenhance synergistically the rigidizing effects of each. For example, acolloidal oxide may be mixed with a filler material in combination withthe placement of an exterior rigidizing means. Such combination mayenhance further the rigidizing effects on a filler or preform.

In a final preferred embodiment of the invention specifically for use inthe formation of metal matrix composite bodies by a spontaneousinfiltration technique, when an infiltration enhancer precursor iscaused to volatilize and react with, for example, an infiltratingatmosphere to form infiltration enhancer in at least a portion of afiller material or preform, the amount of infiltration enhancer that isformed can be minimized so as to reduce any deleterious effects thatsuch formation may have. Particularly, for example, in thealuminum/magnesium/nitrogen system, when magnesium volatilizes andreacts with nitrogen, a magnesium nitride infiltration enhancer isformed in at least a portion of the preform or filler material. Theformation of magnesium nitride, in excessive amounts, could result in avolumetric expansion of the preform or filler material. Such volumetricexpansion could lead to microcracks within a preform or filler material.Accordingly, by controlling time and/or temperature and/or the amount ofinfiltration enhancer precursor and/or amount of infiltratingatmosphere, etc., the amount of infiltration enhancer which is formed ina preform or filler material can be controlled so that just a sufficientamount is manufactured to achieve desirable spontaneous infiltration.

In regard to each of the above-discussed preferred embodiments,specifically in combination with the formation of metal matrixcomposites by a spontaneous infiltration technique, and without wishingto be bound by any particular theory or explanation, when aninfiltration enhancer precursor is utilized in combination with at leastone of the matrix metal, and/or filler material or preform and/orinfiltrating atmosphere, the infiltration enhancer precursor may reactto form an infiltration enhancer which induces or assists molten matrixmetal to spontaneously infiltrate a filler material or preform.Moreover, it appears as though it may be necessary for the precursor tothe infiltration enhancer to be capable of being positioned, located oftransportable to a location which permits the infiltration enhancerprecursor to interact with at least one of the infiltrating atmosphere,and/or the preform of filler material, and/or molten matrix metal. Forexample, in some matrix metal/infiltration enhancerprecursor/infiltrating atmosphere systems, it is desirable for theinfiltration enhancer precursor to volatilize at, near, or in somecases, even somewhat above the temperature at which the matrix metalbecomes molten. Such volatilization may lead to: (1) a reaction of theinfiltration enhancer precursor with the infiltrating atmosphere to agaseous species which enhances wetting of the filler material or preformby the matrix metal; and/or (2) a reaction of the infiltration enhancerprecursor with the infiltrating atmosphere to form a solid, liquid orgaseous infiltration enhancer in at least a portion of the fillermaterial or preform which enhances wetting; and/or (3) a reaction of theinfiltration enhancer precursor within the filler material or preformwhich forms a solid, liquid or gaseous infiltration enhancer in at leasta portion of the filler material or preform which enhances wetting.

Thus, for example, if an infiltration enhancer precursor was included orcombined with, at least at some point during the process, molten matrixmetal, it is possible that the infiltration enhancer precursor couldvolatilize from the molten matrix metal and react with at least one ofthe filler material or preform and/or the infiltrating atmosphere. Suchreaction could result in the formation of an infiltration enhancer whichmay be a solid species, if such solid species was stable at theinfiltration temperature, said solid species being capable of beingdeposited on at least a portion of the filler material or preform as,for example, a coating. Moreover, it is conceivable that such solidspecies could be present as a discernable solid within at least aportion of the preform or filler material. If such a solid species wasformed, molten matrix metal may have a tendency to react with the solidspecies (e.g., the molten matrix metal may reduce the formed solidspecies) such that infiltration enhancer precursor may become associatedwith (e.g., dissolved in or alloyed with) the molten matrix metal.Accordingly, additional infiltration enhancer precursor may then beavailable to volatilize and react with another species (e.g., the fillermaterial or preform and/or infiltrating atmosphere) and again form asimilar solid species. It is conceivable that a continuous process ofconversion of infiltration enhancer precursor to infiltration enhancerfollowed by a reduction reaction of the infiltration enhancer withmolten matrix metal to again form infiltration enhancer, and so on,could occur, until the result achieved is a spontaneously infiltratedmetal matrix composite.

In order to effect spontaneous infiltration of the matrix metal into thefiller material or preform, an infiltration enhancer should be providedto the spontaneous system. An infiltration enhancer could be formed froman infiltration enhancer precursor which could be provided (1) in thematrix metal; and/or (2) in the filler material or preform; and/or (3)from the infiltrating atmosphere; and/or (4) from an external sourceinto the spontaneous system. Moreover, rather than supplying aninfiltration enhancer precursor, an infiltration enhancer may besupplied directly to at least one of the filler material or preform,and/or matrix metal, and/or infiltrating atmosphere. Ultimately, atleast during the spontaneous infiltration, the infiltration enhancershould be located in at least a portion of the filler material orpreform.

In another preferred embodiment of the invention, it is possible thatthe infiltration enhancer precursor can be at least partially reactedwith the infiltrating atmosphere such that the infiltration enhancer canbe formed in at least a portion of the filler material or preform priorto or substantially contiguous with contacting the filler material orpreform with the matrix metal (e.g., if magnesium was the infiltrationenhancer precursor and nitrogen was the infiltrating atmosphere, theinfiltration enhancer could be magnesium nitride which would be locatedin at least a portion of the preform or filler material).

An example of a matrix metal/infiltration enhancerprecursor/infiltrating atmosphere system is thealuminum/magnesium/nitrogen system. Specifically, an aluminum matrixmetal can be contained within a suitable refractory vessel which, underthe process conditions, does not adversely react with the aluminummatrix metal and/or the filler material when the aluminum is mademolten. A filler material or preform can thereafter be contacted withmolten aluminum matrix metal and spontaneously infiltrated.

Moreover, rather than supplying an infiltration enhancer precursor, aninfiltration enhancer may be supplied directly to at least one of thepreform or filler material, and/or matrix metal, and/or infiltratingatmosphere. Ultimately, at least during the spontaneous infiltration,the infiltration enhancer should be located in at least a portion of thefiller material or preform.

Under the conditions employed in the method of the present invention, inthe case of an aluminum/magnesium/nitrogen spontaneous infiltrationsystem, the preform or filler material should be sufficiently permeableto permit the nitrogen-containing gas to penetrate or permeate thefiller material or preform at some point during the process and/orcontact the molten matrix metal. Moreover, the permeable filler materialor preform can accommodate infiltration of the molten matrix metal,thereby causing the nitrogen-permeated preform to be infiltratedspontaneously with molten matrix metal to form a metal matrix compositebody and/or cause the nitrogen to react with an infiltration enhancerprecursor to form infiltration enhancer in the filler material orpreform and thereby result in spontaneous infiltration. The extent ofspontaneous infiltration and formation of the metal matrix compositewill vary with a given set of process conditions, including magnesiumcontent of the aluminum alloy, magnesium content of the preform orfiller material, amount of magnesium nitride in the preform or fillermaterial, the presence of additional alloying elements (e.g., silicon,iron, copper, manganese, chromium, zinc, and the like), average size ofthe filler material (e.g., particle diameter) comprising the preform orthe filler material, surface condition and type of filler material orpreform, nitrogen concentration of the infiltrating atmosphere, timepermitted for infiltration and temperature at which infiltration occurs.For example, for infiltration of the molten aluminum matrix metal tooccur spontaneously, the aluminum can be alloyed with at least about 1percent by weight, and preferably at least about 3 percent by weight,magnesium (which functions as the infiltration enhancer precursor),based on alloy weight. Auxiliary alloying elements, as discussed above,may also be included in the matrix metal to tailor specific propertiesthereof. Additionally, the auxiliary alloying elements may affect theminimum amount of magnesium required in the matrix aluminum metal toresult in spontaneous infiltration of the filler material or preform.Loss of magnesium from the spontaneous system due to, for example,volatilization should not occur to such an extent that no magnesium ispresent to form infiltration enhancer. Thus, it is desirable to utilizea sufficient amount of initial alloying elements to assure thatspontaneous infiltration will not be adversely affected byvolatilization. Still further, the presence of magnesium in both of thepreform (or filler material) and matrix metal or the preform (or fillermaterial) alone may result in a reduction in the required amount ofmagnesium to achieve spontaneous infiltration (discussed in greaterdetail later herein).

The volume percent of nitrogen in the infiltrating atmosphere alsoaffects formation rates of the metal matrix composite body.Specifically, if less than about 10 volume percent of nitrogen ispresent in the atmosphere, very slow or little spontaneous infiltrationwill occur. It has been discovered that it is preferable for at leastabout 50 volume percent of nitrogen to be present in the atmosphere,thereby resulting in, for example, shorter infiltration times due to amuch more rapid rate of infiltration. The infiltrating atmosphere (e.g.,a nitrogen-containing gas) can be supplied directly to the fillermaterial or preform and/or matrix metal, or it may be produced or resultfrom a decomposition of a material.

The minimum magnesium content required for the molten matrix metal toinfiltrate a filler material or preform depends on one or more variablessuch as the processing temperature, time, the presence of auxiliaryalloying elements such as silicon or zinc, the nature of the fillermaterial, the location of the magnesium in one or more components of thespontaneous system, the nitrogen content of the atmosphere, and the rateat which the nitrogen atmosphere flows. Lower temperatures or shorterheating times can be used to obtain complete infiltration as themagnesium content of the alloy and/or preform is increased. Also, for agiven magnesium content, the addition of certain auxiliary alloyingelements such as zinc permits the use of lower temperatures. Forexample, a magnesium content of the matrix metal at the lower end of theoperable range, e.g., from about 1 to 3 weight percent, may be used inconjunction with at least one of the following: an above-minimumprocessing temperature, a high nitrogen concentration, or one or moreauxiliary alloying elements. When no magnesium is added to the preform,alloys containing from about 3 to 5 weight percent magnesium arepreferred on the basis of their general utility over a wide variety ofprocess conditions, with at least about 5 percent being preferred whenlower temperatures and shorter times are employed. Magnesium contents inexcess of about 10 percent by weight of the aluminum alloy may beemployed to moderate the temperature conditions required forinfiltration. The magnesium content may be reduced when used inconjunction with an auxiliary alloying element, but these elements servean auxiliary function only and are used together with at least theabove-specified minimum amount of magnesium. For example, it has beenobserved that there was substantially no infiltration of nominally purealuminum alloyed only with 10 percent silicon at 1000° C. into a beddingof 500 mesh, 39 CRYSTOLON® (99 percent pure silicon carbide from NortonCo.). However, in the presence of magnesium, silicon has been found topromote the infiltration process. As a further example, the amount ofmagnesium varies if it is supplied exclusively to the preform or fillermaterial. It has been discovered that spontaneous infiltration willoccur with a lesser weight percent of magnesium supplied to thespontaneous system when at least some of the total amount of magnesiumsupplied is placed in the preform or filler material. It may bedesirable for a lesser amount of magnesium to be provided in order toprevent the formation of undesirable intermetallics in the metal matrixcomposite body. In the case of a silicon carbide preform, it has beendiscovered that when the preform is contacted with an aluminum matrixmetal, the preform containing at least about 1% by weight magnesium andbeing in the presence of a substantially pure nitrogen atmosphere, thematrix metal spontaneously infiltrates the preform. In the case of analumina preform, the amount of magnesium required to achieve acceptablespontaneous infiltration is slightly higher. Specifically, it has beenfound that when an alumina preform, when contacted with a similaraluminum matrix metal, at about the same temperature as the aluminumthat infiltrated into the silicon carbide preform, and in the presenceof the same nitrogen atmosphere, at least about 3% by weight magnesiummay be required to achieve similar spontaneous infiltration to thatachieved in the silicon carbide preform discussed immediately above.

It is also noted that it is possible to supply to the spontaneous systeminfiltration enhancer precursor and/or infiltration enhancer on asurface of the alloy and/or on a surface of the preform or fillermaterial and/or within the preform or filler material prior toinfiltrating the matrix metal into the filler material or preform (i.e..it may not be necessary for the supplied infiltration enhancer orinfiltration enhancer precursor to be alloyed with the matrix metal, butrather, simply supplied to the spontaneous system). For example, in thealuminum/magnesium/nitrogen system, if the magnesium was applied to asurface of the matrix metal it may be preferred that the surface shouldbe the surface which is closest to, or preferably in contact with, thepermeable mass of filler material or vice versa; or such magnesium couldbe mixed into at least a portion of the preform or filler material.Still further, it is possible that some combination of surfaceapplication, alloying and placement of magnesium into at least a portionof the preform could be used. Such combination of applying infiltrationenhancer(s) and/or infiltration enhancer precursor(s) could result in adecrease in the total weight percent of magnesium needed to promoteinfiltration of the matrix aluminum metal into the preform, as well asachieving lower temperatures at which infiltration can occur. Moreover,the amount of undesirable intermetallics formed due to the presence ofmagnesium could also be minimized.

The use of one or more auxiliary alloying elements and the concentrationof nitrogen in the surrounding gas also affects the extent of nitridingof the matrix metal at a given temperature. For example, auxiliaryalloying elements such as zinc or iron included in the alloy, or placedon a surface of the alloy, may be used to reduce the infiltrationtemperature and thereby decrease the amount of nitride formation,whereas increasing the concentration of nitrogen in the gas may be usedto promote nitride formation.

The concentration of magnesium in the alloy, and/or placed onto asurface of the alloy, and/or combined in the filler material or preform,also tends to affect the extent of infiltration at a given temperature.Consequently, in some cases where little or no magnesium is contacteddirectly with the preform or filler material, it may be preferred thatat least about three weight percent magnesium be included in the alloy.Alloy contents of less than this amount, such as one weight percentmagnesium, may require higher process temperatures or an auxiliaryalloying element for infiltration. The temperature required to effectthe spontaneous infiltration process of this invention may be lower: (1)when the magnesium content of the alloy alone is increased, e.g., to atleast about 5 weight percent; and/or (2) when alloying constituents aremixed with the permeable mass of filler material or preform; and/or (3)when another element such as zinc or iron is present in the aluminumalloy. The temperature also may vary with different filler materials. Ingeneral, in the aluminum/magnesium/nitrogen system spontaneous andprogressive infiltration will occur at a process temperature of at leastabout 675° C., and preferably a process temperature of at least about750° C.-800° C. Temperatures generally in excess of 1200° C. do notappear to benefit the process, and a particularly useful temperaturerange has been found to be from about 675° C. to about 1000° C. However,as a general rule, the spontaneous infiltration temperature is atemperature which is above the melting point of the matrix metal butbelow the volatilization temperature of the matrix metal. Moreover, thespontaneous infiltration temperature should be below the melting pointof the filler material. Still further, as temperature is increased, thetendency to form a reaction product between the matrix metal andinfiltrating atmosphere increases (e.g., in the case of aluminum matrixmetal and a nitrogen infiltrating atmosphere, aluminum nitride may beformed). Such reaction product may be desirable or undesirable basedupon the intended application of the metal matrix composite body.Additionally, electric resistance heating is typically used to achievethe infiltrating temperatures. However, any heating means which cancause the matrix metal to become molten and does not adversely affectspontaneous infiltration, is acceptable for use with the invention.

In the present method, for example, a permeable filler material orpreform comes into contact with molten aluminum in the presence of, atleast sometime during the process, a nitrogen-containing gas. Thenitrogen-containing gas may be supplied by maintaining a continuous flowof gas into contact with at least one of the filler material or preformand/or molten aluminum matrix metal. Although the flow rate of thenitrogen-containing gas is not critical, it is preferred that the flowrate be sufficient to compensate for any nitrogen lost from theatmosphere due to any nitride formation, and also to prevent or inhibitthe incursion of air which can have an oxidizing effect on the moltenmetal.

The method of forming a metal matrix composite is applicable to a widevariety of filler materials, and the choice of filler materials willdepend on such factors as the matrix metal alloy, the processconditions, the reactivity of the molten matrix metal alloy with thefiller material, and the properties sought for the final compositeproduct. For example, when aluminum is the matrix metal, suitable fillermaterials include (a) oxides, e.g. alumina, magnesia, zirconia; (b)carbides, e.g. silicon carbide; (c) borides, e.g. aluminum dodecaboride,titanium diboride, and (d) nitrides, e.g. aluminum nitride, and (e)mixtures thereof. If there is a tendency for the filler material toreact with the molten aluminum matrix metal, this might be accommodatedby minimizing the infiltration time and temperature or by providing anon-reactive coating on the filler. The filler material may comprise asubstrate, such as carbon or other nonceramic material, bearing aceramic coating to protect the substrate from attack or degradation.Suitable ceramic coatings include oxides, carbides, borides andnitrides. Ceramics which are preferred for use in the present methodinclude alumina and silicon carbide in the form of particles, platelets,whiskers and fibers. The fibers can be discontinuous (in chopped form)or in the form of continuous filament, such as multifilament tows.Further, the filler material or preform may be homogeneous orheterogeneous.

It also has been discovered that certain filler materials exhibitenhanced infiltration relative to filler materials having a similarchemical composition. For example, crushed alumina bodies made by themethod disclosed in U.S. Pat. No. 4,713,360, entitled "Novel CeramicMaterials and Methods of Making Same", which issued on Dec. 15, 1987, inthe names of Marc S. Newkirk et al., exhibit desirable infiltrationproperties relative to commercially available alumina products.Moreover, crushed alumina bodies made by the method disclosed in U.S.Pat. No. 4,851,375, entitled "Methods of Making Composite CeramicArticles Having Embedded Filler" in the names of Marc S. Newkirk et al.,also exhibit desirable infiltration properties relative to commerciallyavailable alumina products. The subject matter of each of the issuedPatents is herein expressly incorporated by reference. Thus, it has beendiscovered that complete infiltration of a permeable mass of ceramicmaterial can occur at lower infiltration temperatures and/or lowerinfiltration times by utilizing a crushed or comminuted body produced bythe method of the aforementioned U.S. Patent and Patent Application.

The size, shape, chemistry and volume percent of the filler material (orpreform) can be any that may be required to achieve the propertiesdesired in the composite. Thus, the filler material may be in the formof particles, whiskers, platelets or fibers since infiltration is notrestricted by the shape of the filler material. Other shapes such asspheres, tubules, pellets, refractory fiber cloth, and the like may beemployed. In addition, the size of the filler material does not limitinfiltration, although a higher temperature or longer time period may beneeded for complete infiltration of a mass of smaller particles than forlarger particles or vice-versa depending on the particular reactionconditions. Average particle diameters as small as a micron or less toabout 1100 microns or more can be successfully utilized in the presentinvention, with a range of about 2 microns through about 1000 micronsbeing preferred for a vast majority of commercial applications. Further,the mass of filler material (or preform) to be infiltrated should bepermeable (i.e., contain at least some interconnected porosity to renderit permeable to molten matrix metal and/or to the infiltratingatmosphere). Moreover, by controlling the size (e.g., particle diameter)and/or geometry and/or composition of the filler material or thematerial comprising the preform, the physical and mechanical propertiesof the formed metal matrix composite can be controlled or engineered tomeet any number of industrial needs. For example, wear resistance of themetal matrix composite can be increased by increasing the size of thefiller material (e.g., increasing the average diameter of the fillermaterial particles) given that the filler material has a higher wearresistance than the matrix metal. However, strength and/or toughness maytend to increase with decreasing filler size. Further, the thermalexpansion coefficient of the metal matrix composite may decrease withincreasing filler loading, given that the coefficient of thermalexpansion of the filler is lower than the coefficient of thermalexpansion of the matrix metal. Still further, the mechanical and/orphysical properties (e.g., density, coefficient of thermal expansion,elastic and/or specific modulus, strength and/or specific strength,etc.) of a formed metal matrix composite body may be tailored dependingon the loading of the filler material in the loose mass or in thepreform. For example, by providing a loose mass or preform comprising amixture of filler particles of varying sizes and/or shapes, wherein thedensity of the filler is greater than that of the matrix metal, a higherfiller loading, due to enhanced packing of the filler materials, may beachieved, thereby resulting in a metal matrix composite body with anincreased density. By utilizing the teachings of the present invention,the volume percent of filler material or preform which can beinfiltrated can vary over a wide range. The lower volume percent offiller that can be infiltrated is limited primarily by the ability toform a porous filler material or preform, (e.g., about 10 volumepercent); whereas the higher volume percent of filler or preform thatcan be infiltrated is limited primarily by the ability to form a densefiller material or preform with at least some interconnected porosity(e.g., about 95 volume percent). Accordingly, by practicing any of theabove teachings, at one or in combination, a metal matrix composite canbe engineered to contain a desired combination of properties.

The method of forming metal matrix composites according to the presentinvention, not being dependent on the use of pressure to force orsqueeze molten matrix metal into a rigidized preform or a rigidized massof filler material, permits the production of substantially uniformmetal matrix composites having a high volume fraction of filler materialand low porosity. Higher volume fractions of filler material may beachieved by using a lower porosity initial mass of filler material.Higher volume fractions also may be achieved if the mass of filler iscompacted or otherwise densified prior to rigidizing provided that themass is not converted into either a compact with closed cell porosity orinto a fully dense structure that would prevent infiltration by themolten alloy. Specifically, volume fractions on the order of about 60 to80 volume percent can be achieved by methods such as vibrationalpacking, controlling particle size distribution, etc. However,alternative techniques can be utilized to achieve even higher volumefractions of filler. Volume fractions of filler on the order of 40 to 50percent are preferred for thermo-forming metal matrix composite bodiesin accordance with the present invention. At such volume fractions, theinfiltrated composite maintains or substantially maintains its shape,thereby facilitating secondary processing. Higher or lower particleloadings or volume fractions could be used, however, depending on thedesired final composite loading after thermo-forming. Moreover, methodsfor reducing particle loadings can be employed in connection with thethermo-forming processes of the present invention to achieve lowerparticle loadings.

It has been observed that for aluminum infiltration and matrix formationaround a ceramic filler, wetting of the ceramic filler by the aluminummatrix metal may be an important part of the infiltration mechanism.Further, the wetting of the filler by molten matrix metal may permit auniform dispersion of the filler throughout the formed metal matrixcomposite and improve the bonding of the filler to the matrix metal.Moreover, at low processing temperatures, a negligible or minimal amountof metal nitriding occurs resulting in a minimal discontinuous phase ofaluminum nitride dispersed in the metal matrix. However, as the upperend of the temperature range is approached, nitridation of the metal ismore likely to occur. Thus, the amount of the nitride phase in the metalmatrix can be controlled by varying the processing temperature at whichinfiltration occurs. The specific process temperature at which nitrideformation becomes more pronounced also varies with such factors as thematrix aluminum alloy used and its quantity relative to the volume offiller or preform, the filler material to be infiltrated, and thenitrogen concentration of the infiltrating atmosphere. For example, theextent of aluminum nitride formation at a given process temperature isbelieved to increase as the ability of the alloy to wet the fillerdecreases and as the nitrogen concentration of the atmosphere increases.

It is therefore possible to tailor the constituency of the metal matrixduring formation of the composite to impart certain characteristics tothe resulting product. For a given system, the process conditions can beselected to control the nitride formation. A composite productcontaining an aluminum nitride phase will exhibit certain propertieswhich can be favorable to, or improve the performance of, the product.Further, the temperature range for spontaneous infiltration with analuminum alloy may vary with the ceramic material used. In the case ofalumina as the filler material, the temperature for infiltration shouldpreferably not exceed about 1000° C. if it is desired that the ductilityof the matrix not be reduced by the significant formation of nitride.However, temperatures exceeding 1000° C. may be employed if it isdesired to produce a composite with a less ductile and stiffer matrix.To infiltrate silicon carbide, higher temperatures of about 1200° C. maybe employed since the aluminum alloy nitrides to a lesser extent,relative to the use of alumina as filler, when silicon carbide isemployed as a filler material.

Further, the constituency of the matrix metal within the metal matrixcomposite and defects, for example, porosity, may be modified bycontrolling the cooling rate of the metal matrix composite. For example,the metal matrix composite may be directionally solidified by any numberof techniques including: placing the container holding the metal matrixcomposite upon a chill plate; and/or selectively placing insulatingmaterials about the container. Further, the constituency of the metalmatrix may be modified after formation of the metal matrix composite.For example, exposure of the formed metal matrix composite to a heattreatment may improve the tensile strength of the metal matrixcomposite. (The standard test for tensile strength is ASTM-D3552-77(reapproved 1982).)

For example, a desirable heat treatment for a metal matrix compositecontaining a 520.0 aluminum alloy as the matrix metal may compriseheating the metal matrix composite to an elevated temperature, forexample, to about 430° C., which is maintained for an extended period(e.g., 18-20 hours). The metal matrix may then be quenched in boilingwater at about 100° C. for about 20 seconds (i.e., a T-4 heat treatment)which can temper or improve the ability of the composite to withstandtensile stresses.

Moreover, it is possible to use a reservoir of matrix metal to assurecomplete infiltration of the filler material or preform and/or to supplya second metal which has a different composition from the first sourceof matrix metal. Specifically, in some cases it may be desirable toutilize a matrix metal in the reservoir which differs in compositionfrom the first source of matrix metal. For example, if an aluminum alloyis used as the first source of matrix metal, then virtually any othermetal or metal alloy which was molten at the processing temperaturecould be used as the reservoir metal. Molten metals frequently are verymiscible with each other which would result in the reservoir metalmixing with the first source of matrix metal so long as an adequateamount of time is given for the mixing to occur. Thus, by using areservoir metal which is different in composition from the first sourceof matrix metal, it is possible to tailor the properties of the metalmatrix to meet various operating requirements and thus tailor theproperties of the metal matrix composite.

A barrier means may also be utilized in combination with the presentinvention. Specifically, the barrier means for use with this inventionmay be any suitable means which interferes, inhibits, prevents orterminates the migration, movement, or the like, of molten matrix alloy(e.g., an aluminum alloy) beyond the defined surface boundary of thefiller material. Suitable barrier means may be any material, compound,element, composition, or the like, which, under the process conditionsof this invention, maintains some integrity, is not volatile andpreferably is permeable to the gas used with the process, as well asbeing capable of locally inhibiting, stopping, interfering with,preventing, or the like, continued infiltration or any other kind ofmovement beyond the defined surface boundary of the ceramic filler.Barrier means may be used during spontaneous infiltration or in anymolds or other fixtures utilized in connection with thermo-forming ofthe spontaneously infiltrated metal matrix composite, as discussed ingreater detail below.

Suitable barrier means include materials which are substantiallynon-wettable by the migrating molten matrix alloy under the processconditions employed. A barrier of this type appears to exhibit little orno affinity for the molten matrix alloy, and movement beyond the definedsurface boundary of the filler material or preform is prevented orinhibited by the barrier means. The barrier reduces any final machiningor grinding that may be required of the metal matrix composite product.As stated above, the barrier preferably should be permeable or porous,or rendered permeable by puncturing, to permit the gas to contact themolten matrix alloy.

Suitable barriers particularly useful for aluminum matrix alloys arethose containing carbon, especially the crystalline allotropic form ofcarbon known as graphite. Graphite is essentially non-wettable by themolten aluminum alloy under the described process conditions. Aparticular preferred graphite is a graphite foil product that is soldunder the trademark GRAFOIL®, registered to Union Carbide. This graphitefoil exhibits sealing characteristics that prevent the migration ofmolten aluminum alloy beyond the defined surface boundary of the fillermaterial. This graphite foil is also resistant-to heat and is chemicallyinert. GRAFOIL® graphite foil is flexible, compatible, conformable andresilient. It can be made into a variety of shapes to fit any barrierapplication. However, graphite barrier means may be employed as a slurryor paste or even as a paint film around and on the boundary of thefiller material or preform. GRAFOIL® is particularly preferred becauseit is in the form of a flexible graphite sheet. In use, this paper-likegraphite is simply formed around the filler material or preform.

Other preferred barrier(s) for aluminum metal matrix alloys in nitrogenare the transition metal borides (e.g., titanium diboride (TiB₂)) whichare generally non-wettable by the molten aluminum metal alloy undercertain of the process conditions employed using this material. With abarrier of this type, the process temperature should not exceed about875° C., for otherwise the barrier material becomes less efficaciousand, in fact, with increased temperature infiltration into the barrierwill occur. Moreover, the particle size of the barrier material mayaffect the ability of the material to inhibit spontaneous infiltration.The transition metal borides are typically in a particulate form (1-30microns). The barrier materials may be applied as a slurry or paste tothe boundaries of the permeable mass of ceramic filler material whichpreferably is preshaped as a preform.

Other useful barriers for aluminum metal matrix alloys in nitrogeninclude low-volatile organic Compounds applied as a film or layer ontothe external surface of the filler material or preform. Upon firing innitrogen, especially at the process conditions of this invention, theorganic compound decomposes leaving a carbon soot film. The organiccompound may be applied by conventional means such as painting,spraying, dipping, etc.

Moreover, finely ground particulate materials can function as a barrierso long as infiltration of the particulate material would occur at arate which is slower than the rate of infiltration of the fillermaterial.

Thus, the barrier means may be applied by any suitable means, such as bycovering the defined surface boundary with a layer of the barrier means.Such a layer of barrier means may be applied by painting, dipping, silkscreening, evaporating, or otherwise applying the barrier means inliquid, slurry, or paste form, or by sputtering a vaporizable barriermeans, or by simply depositing a layer of a solid particulate barriermeans, or by applying a solid thin sheet or film of barrier means ontothe defined surface boundary. With the barrier means in place,spontaneous infiltration substantially terminates when the infiltratingmatrix metal reaches the defined surface boundary and contacts thebarrier means.

Various demonstrations of the present invention are included in theExamples immediately following. However, these Examples should beconsidered as being illustrative and should not be construed as limitingthe scope of the invention as defined in the appended claims.

EXAMPLE 1

This Example demonstrates that through the use of a colloidal aluminarefractory high temperature binder in a preform that any preformexpansion which might otherwise occur during spontaneous infiltrationwithout the use of the colloidal alumina in the preform can be reducedor even substantially completely eliminated.

An aqueous solution of BLUONIC® A colloidal alumina (BuntrockIndustries, Inc., Lively, Va.) totaling about 261 grams was diluted withabout 523 grams of water and placed into a 2 liter NALGENE® plastic jar(Nalge Company, Rochester, N.Y.). About 1281 grams of 220 grit 39CRYSTOLON® green silicon carbide particulate (Norton Company, Worcester,Mass.) and about 549 grams of 500 grit 39 CRYSTOLON® green siliconcarbide particulate were added to the jar to prepare a slurry forsediment casting. The total slurry weight was about 2615 grams and theslurry comprised by weight about 4g percent 220 grit silicon carbide,about 21 percent 500 grit silicon carbide, about 2 percent colloidalalumina (dry basis) and about 28 percent water. After roll mixing theslurry in the plastic jar for about 45 minutes, the slurry was pouredinto a Grade GI-1000 silicone rubber mold (Plastic Tooling Supply Co.,Exton, Pa.) having an internal cavity measuring about 3 inches (76 mm)square and about 11/2 inches (38 mm) deep. The mold was vibrated toassist in sedimentation. After vibrating for about 1/2 hour, the excesswater on the surface of the formed sediment cast preform was removedwith a paper towel. After vibrating for an additional 1 to 11/2 hours,the remaining surface water was removed and the silicone rubber mold wasremoved from the vibration table and placed into a freezer. Residualwater in the preform was permitted to freeze thoroughly, then thesilicone rubber mold and its preform were removed from the freezer andthe frozen sediment cast preform was withdrawn from the mold. Thepreform was then placed on a bed of 90 grit 38 ALUNDUM® aluminaparticulate material (Norton Company) and allowed to dry in air at roomtemperature for about 16 hours.

After drying, the sediment cast preform was transferred to a differentbedding of 90 grit 38 ALUNDUM® alumina supported by a refractory platemeasuring about 12 inches (305 mm) long by about 6 inches (152 mm) wideby about 1 inch (25 mm) thick and placed into a resistance heated airatmosphere furnace. The furnace temperature was increased from aboutroom temperature to a temperature of about 1050° C. in a period of about10 hours. After maintaining a temperature of about 1050° C. for about 2hours, the temperature was decreased to about room temperature in aperiod of about 10 hours.

As shown in FIG. 1, a graphite foil box 52 measuring about 4 inches (102mm) square and about 3 inches (76 mm) tall was fabricated from a singlesheet of GRAFOIL® graphite foil (Union Carbide Company, Danbury, Conn.)measuring about 0.015 inches (0.38 mm) thick by making strategicallylocated cuts and folds in the sheet. The folds in the GRAFOIL® sheetwere cemented together with RIGIDLOCK® graphite cement (PolycarbonCorporation, Valencia, Calif.). Strategically placed staples helped toreinforce the graphite cement. The GRAFOIL® box 52 was then placedwithin a graphite boat 50, said graphite boat 50 having interiordimensions substantially the same as the box 52. The fired preform 58was then placed into the bottom of the GRAFOIL® box 52. About 0.36 gramof magnesium particulate 60 (-100 mesh, Hart Corporation, Tamaqua, Pa.)was sprinkled evenly over the top surface of the fired preform 58. Agating means 62, 64 comprising a sheet of GRAFOIL® 62 measuring about 4inches (102 mm) square with an approximately 11/2 inch (38 mm) diameterhole cut in the center, was cemented with RIGIDLOCK® graphite cement toa graphite riser ring 64 measuring about 3/8 inch (10 mm) tall and about11/2 inches (38 mm) in inside diameter such that the inside diameter ofthe ring substantially coincided with the hole in the GRAFOIL® sheet 62.The gating means 62, 64 was then placed into the GRAFOIL® box 52 on topof the layer of magnesium particulate 60 and oriented such that theGRAFOIL® sheet 62 contacted the magnesium particulate layer 60 and thegraphite riser ring 64 was on a top surface of the GRAFOIL® sheet 62.The cavity inside the graphite riser ring 64 was filled with anadmixture 66 comprising by weight about 50 percent magnesium particulate(-100 mesh, Hart Corporation), about 1 percent magnesium particulate(-325 mesh, Hart Corporation), about 25 percent 54 grit 39 CRYSTOLON®green silicon carbide particulate (Norton Company) and about 24 percent90 grit 39 CRYSTOLON® green silicon carbide particulate. A beddingmaterial admixture 68 Comprising by weight about 15 percent Grade P-941glass frit (Industrial Chemicals Division of Mobay Chemical Corporation,Baltimore, Md.) and the balance equal weight fractions of 90 grit, 220grit, and 500 grit E1ALUNDUM® alumina (Norton Company) was poured intothe GRAFOIL® box 52 on the GRAFOIL® sheet 62 around the graphite riserring 64 to a level substantially flush with the top of the ring 64 butslightly higher out towards the walls of the GRAFOIL® box 52. A matrixmetal ingot 70 weighing about 300 grams and measuring about 2 inches (51mm) square and about 13/4 inches (44 mm) tall and comprising by weightabout 15 percent silicon, about 5 percent magnesium and the balancealuminum, was placed into the GRAFOIL® box 52 and centered over thegraphite riser ring 64 to form a lay-up.

The graphite boat 50 and its contents were placed into a resistanceheaded controlled atmosphere furnace at substantially room temperature.The furnace was sealed, evacuated to about 30 inches (762 mm) of mercuryvacuum, and backfilled with nitrogen gas to about atmospheric pressure.A nitrogen gas flow rate of about 4 liters per minute was established.The temperature in the furnace was then increased to about 825° C. at arate of about 150° C. per hour. After maintaining a temperature of about825° C. for about 10 hours, the temperature was then decreased to about700° C. at a rate of about 200° C. per hour. At a temperature of about700° C., the furnace was opened and the graphite boat 50 and itscontents were removed and placed onto a water cooled aluminum quenchplate. FEEDOL® No. 9 hot topping particulate mixture was poured onto theresidual molten matrix metal to directionally solidify the matrix metalin the metal matrix composite body. After the bulk of the exothermic hottopping reaction had subsided, the top and sides of the graphite boat 50were covered with an approximately 2 inch (51 mm) thick layer ofCERABLANKET® ceramic fiber insulation material to assist in thedirectional solidification of the matrix metal. After cooling tosubstantially room temperature, the GRAFOIL® box 52 was removed from thegraphite boat 50 and was disassembled to reveal that the matrix metalhad infiltrated the preform to produce a metal matrix composite body.The residual matrix metal was separated from the remainder of the lay-upby using moderate hand pressure. The bedding material admixture 68 wasremoved with light hammer blows. The graphite riser ring 64 and itsattached GRAFOIL® sheet 62 were removed by sandblasting. Measurement ofthe dimensions of the formed metal matrix composite using a pair ofcalipers revealed that substantially no dimensional change had takenplace during the spontaneous infiltration process. Thus, this Exampleillustrates that the use of a refractory binder comprising colloidalalumina permits the formation of a metal matrix composite body whichsubstantially identically replicates the shape of the preform.

EXAMPLE 2

This Example demonstrates that through the use of a colloidal aluminarefractory high temperature binder in a preform that any preformexpansion which may otherwise occur during spontaneous infiltrationwithout the use of the colloidal alumina in the preform can be reducedor even substantially completely eliminated.

Two preforms, each preform having approximate measurements of 7 inches(178 mm) by 7 inches (178 mm) by 0.5 inch (13 mm), were sediment castfrom a mixture of a 220 grit alumina material known by the trade name 38ALUNDUM° and produced by Norton Co., and colloidal alumina (NyacolAL-20). The approximate weight ratio of the colloidal alumina to the 220grit 38 ALUNDUM®was 70/30.

After the preforms had dried and set, a thin (approximately 1/64 inch(0.4 mm) thick) layer of colloidal alumina paste (Nyacol AL-20) waspainted on a surface of each of the two preforms. The two paintedsurfaces were then brought into contact so as to sandwich the colloidalalumina between the two preforms. As shown in FIG. 2, this assembly ofpreforms 80, including the interfacial layer 81 of colloidal alumina,was then placed within a refractory boat 82 on top of an approximately1/2 inch (13 mm) thick layer of Grade HCT titanium diboride 86 producedby Union Carbide. An ingot 84 of matrix metal having approximatedimensions of 7 inches (178 mm) by 7 inches (178 mm) by 1/2 inch (13 mm)and comprising by weight approximately 5% silicon, 5% zinc, 7% Mg, 2%copper and the balance aluminum was placed on top of the assembly ofpreforms 80. Additional Grade HCT titanium diboride was then added tothe refractory boat 82 until the surface of the bed 86 of titaniumdiboride was approximately level with the upper surface of the matrixmetal ingot 84.

The setup, consisting of the refractory boat 82 and its contents wasthen placed within a controlled atmosphere electric resistance heatedvacuum furnace at room temperature. A high vacuum (approximately 1×10-4torr) was then achieved within the furnace and the furnace temperaturewas raised to about 200° C. in about 45 minutes. The furnace temperaturewas maintained at about 200° C. under vacuum conditions forapproximately 2 hours. After this initial two hour heating period, thefurnace was backfilled with nitrogen gas to approximately 1 atmosphereand the temperature was raised to about 865° C. in approximately 5hours; maintained at about 865° C. for about 18 hours; and then rampedto room temperature in about 5 hours.

After reaching room temperature, the setup was removed from the furnaceand disassembled. It was observed that the formed metal matrix compositebody corresponded in size and shape to the preform.

EXAMPLE 3

This Example demonstrates that through the use of a colloidal silicarefractory high temperature binder in a mold surrounding a preform, thatany preform expansion which may otherwise occur during spontaneousinfiltration without the use of the colloidal silica in the mold can bereduced or even substantially completely eliminated.

As shown in FIG. 3, a silica mold 111 having an inner diameter ofapproximately 5 inches (127 mm) by 5 inches (127 mm) and 31/4 inches (83mm) in height, and having nine holes of about 3/4 inch (19 mm) diameterand 3/4 inch (19 mm) depth in the bottom of the mold 111, was formed byfirst mixing a slurry of about 2.5 to 3 parts by weight of RANCO-SIL™ 4silica powder, about 1 part by weight colloidal silica (Nyacol 830 fromNyacol Products of Ashland, Mass.) and about 1 to 1.5 parts by weight ofRANCO-SIL™ A silica sand (Ransom and Randoll of Maumee, Ohio). Theslurry was poured into a rubber mold having the negative shape of thedesired silica mold and placed in a freezer overnight. The silica moldwas subsequently removed from the rubber mold, fired at about 800° C. inan air furnace for about 1 hour and allowed to cool to room temperature.

The bottom surface of the formed silica mold 111 was covered with anapproximately 5 inch (127 mm) by 5 inch (127 mm) by 0.010 inch (6.25 mm)thick PF-25-H graphite tape product 117, sold by TTAmerica, Portland,Oreg., under the trade name PERMA FOIL®, having approximately 3/4 inch(19 mm) diameter holes 118 cut into the graphite tape sheet 117 tocorrespond in position to the holes in the bottom of the silica mold111. The holes in the bottom of the mold 111 were filled withapproximately 3/4 inch (19 mm) diameter by 3/4 inch (19 mm) thick plugs114 of a metal identical in composition to the matrix metal alloy whichcomprised approximately 10% by weight magnesium and the balancealuminum. Approximately 819 grams of a 500 grit alumina 11er materialknown as 38 ALUNDUM® and produced by Norton Company, was mixed withabout 5 weight percent magnesium powder and shaken for about 15 minutesin a NALGENE® jar. The filler material mixture was then placed into themold 111 to a depth of approximately 3/4 inch (19 mm) and tamped lightlyto level the surface of the filler material mixture 112. A matrix metalingot 113 weighing approximately 1399 grams and comprising about 10% byweight magnesium and the balance aluminum, was placed on top of thefiller material mixture 112 within the silica mold 111. The mold 111 andits contents were then placed into an approximately 10 inch (254 mm) by10 inch (254 mm) by 8 inch (203 mm) high stainless steel container 150.A titanium sponge material 152, weighing about 20 grams, from ChemalloyCompany Inc., Bryn Mawr, Pa., was sprinkled into the stainless steelcontainer 150 around the silica mold 111. A sheet of copper foil 151 wasplaced over the exposed surface of the stainless steel container 150 soas to form an isolated chamber. A nitrogen purge tube 153 was providedthrough the sheet of copper foil 151, and the stainless steel container150 and its contents were placed into an air atmosphere resistanceheated Unique utility box furnace. The system was ramped from roomtemperature to about 600° C. at a rate of about 400° C. per hour with anitrogen flow rate of about 10 liters per minute, then heated from about600° C. to about 775° C. at a rate of about 400° C. per hour with anitrogen flow rate of about 2 liters per minute. The system was held atabout 775° C. for about 1.5 hours with a nitrogen flow rate of about 2liters per minute. The system was removed from the furnace at about 775°C., a substantial portion of the excess molten alloy was poured out, anda room temperature copper chill plate having dimensions of approximately5 inches (127 mm) by 5 inches (127 mm) by 1 inch (13 mm) thick wasplaced within the silica mold 111 such that it contacted a top portionof any remaining matrix metal 113, to directionally cool the formedcomposite.

Upon removal from the silica mold, it was observed that the formed metalmatrix composite body corresponded in size and shape to the preform.

EXAMPLE 4

A tape cast silicon carbide preform, obtained from Keramos Industries,Inc., Morrisville, Pa., having dimensions of about 8 inches (203 mm) byabout 7 inches (177 mm) by about 0.145 inch (4.mm) thick and comprisingby weight about 70% 220 grit, 10% 500 grit, 10% 800 grit, and 10% 1000grit 3 g CRYSTOLON® green silicon carbide particulate (Norton Company,Worcester, Mass.) was placed, with its flatest side facing down, on aperforated cordierite plate. The preform was covered with a sheet ofFIBERFRAX® 907-J fiber insulation paper (The Carborundum Company,Niagara Falls, N.Y.). A second cordierite plate was placed on top of thefiber insulation paper to form an assembly. The assembly was placedwithin a room temperature air atmosphere furnace. The temperature in thefurnace was increased from about room temperature to about 425° C. at arate of about 50° C. per hour. After reaching a temperature of about425° C., the temperature in the furnace was increased to about 1050° C.at a rate of about 200° C. per hour. After maintaining a temperature ofabout 1050° C. for about 1 hour, the temperature in the furnace wasdecreased to about room temperature in about 5 hours. The preform wasremoved from the furnace, and it was observed that the preform hadsintered and formed a three-dimensional rigidized body. The preform wasplaced on a balance, and a preform weight of about 257.04 grams wasrecorded.

The preform was placed on a rotatable platform with its flat side facingup. A first edge and the flat side of the preform were spray coated withKRYLON® acrylic spray coating (Borden, Inc., Columbus, Ohio). Therotatable platform and preform were rotated 90° and a second edge of thepreform and the flat side were spray coated with KRYLON® acrylic spraycoating. This procedure was repeated until all four edges of the preformwere spray coated: with one coat of KRYLON® acrylic spray coating andthe flat side of thereform was coated with four coats of KRYLON® acrylicspray coating. A temperature of about 65° C. was established within anair atmosphere furnace, and the preform was transferred from therotatable platform to the air atmosphere furnace. After about 10minutes, the preform was removed from the air atmosphere furnace andplaced under a fume hood until the coating had substantially dried. Thepreform was removed from the fume hood, placed on a balance, and apreform weight of about 257.22 grams was recorded.

A mixture comprising by volume about 50% DAG® 154 colloidal graphite(Acheson Colloids, Port Huron, Mich.) and about 50% denatured ethanolwas prepared. The preform was placed on a rotatable platform with itsflat side facing up, and an air brush was used to apply a thin layer ofthe mixture to a first edge and the flat side of the preform. Theplatform and preform were rotated 90° and the mixture was applied to asecond edge and the flat side of the preform. This procedure wasrepeated until all four edges of the preform were coated with two coatsand the flat side of the preform was coated with eight coats of themixture, although due to overspray and run-off of the mixture during thecoating of the flat side of the preform, the thickness of the coatingson the edges approximately equalled the thickness of the coating on theflat side of the preform. The preform was then allowed to dry. After thepreform was substantially dry, the preform was placed on a balance and apreform weight of about 257.92 grams was recorded. The preform wasplaced on a rotatable platform with the flat side facing down. Thepreform was spray coated with KRYLON® acrylic spray coating in a mannersubstantially the same as for the KRYLON® coating described above. Atemperature of about 65° C. was established within an air atmospherefurnace, and the preform was transferred from the rotatable platform tothe air atmosphere furnace and then heated for about 10 minutes. Thepreform was removed from the air atmosphere furnace and placed under afume hood. After the preform had substantially dried, the preform wasplaced on a balance and a preform weight of about 258.27 grams wasrecorded. The preform was then placed, with its flat side facing down,on a rotatable platform and an air brush was used to apply a thin layerof the mixture to the top portion of the preform. The mixture was thenallowed to dry completely. A total of three coatings were applied inthis manner, then the preform was placed on a balance and a preformweight of about 259.23 grams was recorded.

As shown in FIG. 4, a sheet of GRAFOIL® graphite foil 22 (Union CarbideCompany, Danbury, Conn.) measuring about 131/4 inches (337 mm) by about91/4 inches (235 mm) by about 0.015 inch (0.4 mm) thick was placed intothe bottom of a graphite boat 21 having inner dimensions of about 131/4inches (337 mm) by about 91/4 inches (235 mm) by about 1 inch (25 mm)high. An about 3/8 inch (9 mm) thick layer of bedding material 23,comprising by weight about 10% F-69 borosilicate glass frit (FusionCeramics, Inc., Carrollton, Ohio) and the balance comprising about 70%by weight 36 grit and about 30% by weight 60 grit E-38 ALUNDUM° alumina(Norton Company, Worcester, Mass.) was poured into the graphite boat 21on top of the GRAFOIL® sheet 22. A foam brush was used to establish alevel layer of bedding material 23.

A matrix metal ingot 24 weighing about 1462.92 grams and comprising byweight about 20% silicon, 5% magnesium and the balance aluminum, wasplaced into an ethanol bath. The surface of the matrix metal ingot 24was cleaned by hand utilizing a paper towel, then the matrix metal ingot24 was removed from the ethanol bath and placed within an air atmospherefurnace. A temperature of about 68° C. was established within thefurnace, and after heating the matrix metal ingot for about 15 minutes,the matrix metal ingot 24 was removed from the furnace and placed on topof the bedding material 23 within the graphite boat 21. Additionalbedding material 23 was poured into the graphite boat 21 around thematrix metal ingot 24 to a level substantially the same as the topportion of the matrix metal ingot 24. A sheet of GRAFOIL® graphite foil(Union Carbide Company, Danbury, Conn.) measuring about 81/4 inches (210mm) by about 71/4 inches (184 mm) by about 0.005 inches (0.1 mm) thickwas prepared by first cutting a rectangular hole measuring about 77/8inches (200 mm) by about 67/8 inches (175 mm) in the center of theGRAFOIL® sheet to produce a GRAFOIL® frame 25. One side of the GRAFOIL®frame 25 was spray coated with KRYLON® acrylic spray coating. TheGRAFOIL® frame was then centered on top of the matrix metal ingot 24with the acrylic coating in contact with the matrix metal ingot 24. Theportion of the matrix metal ingot 24 within the inner boundaries of theGRAFOIL® frame 25 was spray coated with KRYLON® acrylic spray coating.About 5.6 grams of -50 mesh atomized magnesium 27 {Hart Corporation,Tamaqua, Pa.) was sprinkled onto the portion of the matrix metal ingot24 within the inner boundaries of the GRAFOIL® frame 25. The GRAFOIL®frame 25, the -50 mesh atomized magnesium 27 and the matrix metal ingot24 were then spray coated with KRYLON® acrylic spray coating, and theacrylic spray coating was allowed to dry for about 3 minutes. Thepreform 26 was centered on top of the GRAFOIL® frame 25, with the flatside of the preform 26 in contact with the GRAFOIL® frame 25, the -50mesh atomized magnesium 27 and the matrix metal ingot 24.

The graphite boat 21 and its contents were placed into a resistanceheated controlled atmosphere furnace at about room temperature. Thefurnace was sealed, evacuated to about 30 inches (762 mm) of mercuryvacuum, and backfilled with nitrogen gas to about atmospheric pressure.A nitrogen gas flow rate of about 5 liters per minute was establishedwithin the furnace. The temperature in the furnace was increased fromabout room temperature to about 225° C. at a rate Of about 200° C. perhour. After maintaining a temperature of about 225° C. for about 52hours, the temperature in the furnace was increased to about 850° C. ata rate of about 200° C. per hour. After maintaining a temperature ofabout 850° C. for about 10 hours, the temperature in the furnace wasdecreased to about 825° C. at a rate of about 200° C. per hour. Thegraphite boat 21 and its contents were then removed from the furnace. Anabout 15 inch (381 mm) by about 11 inch (27g mm) by about 2 inch (51 mm)thick layer of CERABLANKET® ceramic insulation material (ManvilleRefractory Products, Denver, Colo.) was placed onto a graphite table. Asingle sheet of GRAFOIL° graphite foil having dimensions of about 15inches (381 mm) by about 11 inches (279 mm) by about 0.015 inch (0.38ram) thick was placed on top of the CERABLANKET® fiber insulationmaterial. The graphite boat 21 and its contents were placed on top ofthe GRAFOIL® graphite foil and allowed to cool. After about 13 minutes,light chisel blows were applied to the solidified carcass of matrixmetal causing the formed metal matrix composite to separate from thematrix metal. Thus, this example demonstrates that a rigidized fillermaterial may be spontaneously infiltrated by a molten matrix metal inaccordance with the present invention.

EXAMPLE 5

This Example further demonstrates that a rigidized filler material maybe spontaneously infiltrated by a molten matrix metal to yield a metalmatrix composite body. Specifically, about 166.5 grams of a mixturecomprising by weight about 30% AIRVOL® PVA (Air Products and Chemicals,Inc., Allentown, Pa.) and about 70% deionized water was placed into aplastic jar. About 24.9 grams of polyethylene glycol 400 (J. T. Baker,Inc., Jackson, Tenn.), about 2.4 grams of zinc stearate (FischerScientific, Pittsburgh, Pa.) and about 106.2 grams of LUDOX® SMcolloidal silica (E. I. DuPont DeNemours and Co., Inc., Wilmington,Del.) were added to the jar. A hand-held drill with an impellerattachment was used to thoroughly mix the contents of the jar to preparea binder solution.

About 1750 grams of 320 grit, about 250 grams of 800 grit, and about 250grams of 1000 grit 39 CRYSTOLON® green silicon carbide particulate(Norton Company, Worcester, Mass.) were added to a one gallon plasticjar (Fischer Scientific, Pittsburgh, Pa.). About 250 grams of LC12N Si₃N₄ powder (Herman C. Stark, Berlin, Germany) were added to the jar andthe plastic jar and its contents were mixed on a jar mill for about twohours. The plastic jar and its contents were then removed from the jarmill and the contents of the jar were poured into a Model RV02 Eirichmixer (Eirich Machines, Maple, Ontario, Canada). About 100 grams of thebinder solution were poured into the Eirich mixer. The mixer was turnedon with the pan and rotor settings set to fast. After about one minute,the mixer was turned off, a plastic straight edge was utilized to removeany silicon carbide particulate or silicon nitride powder from the sidesof the mixer bowl, and an additional about 100 grams of binder solutionwas added to the mixer. The mixer was turned on a second time with thepan and rotor settings set to fast. After about one minute, the mixerwas turned off, a plastic straight edge was used to scrape any siliconcarbide particulate or silicon nitride powder from the sides of thebowl, and an additional about 100 grams of binder solution was added tothe mixer. The mixer was turned on a third time with the pan and rotorsettings set to fast. After about one minute, the mixer was turned offand the binder/silicon carbide particulate/silicon nitride powdermixture was poured onto a table that had been previously covered withbrown paper. An about 1/8 inch (3 mm) to about 1/4 inch (6 mm) thicklayer of the mixture was established on the brown paper and the mixturewas allowed to dry overnight.

The mixture was placed into a Model B Ro-tap testing sieve shaker (TylerCombustion Engineering, Inc.) and sifted through a 25 mesh screen. About160 grams of the mixture was placed into a die mold having dimensions ofabout 3 inches (76 mm) square and pressed at about 90 tons of pressureutilizing a CARVER® air type hydraulic press (Fred S. Carver, Inc.,Menomonee Falls, Wisc.). The resultant preform was removed from thehydraulic press and the preform dimensions, measuring about 3 inches (76mm) square by about 1/2 inch (13 mm) thick, were recorded. A total offour preforms were prepared in this manner.

The preforms were-then placed onto a refractory support plate, which hadbeen covered with a sheet of FIBERFRAX® 907-J fiber insulation paper(The Carborundum Company, Niagara Falls, N.Y.). The supported preformswere placed into a room temperature resistance heated air atmospherefurnace. The furnace temperature was raised from about room temperatureto about 500° C. at a rate of about 100° C. per hour. After maintaininga temperature of about 500° C. for about two hours, the temperature wasthen increased from about 500° C. to about 850° C. at a rate of about200° C. per hour. After maintaining a temperature of about 850° C. forabout four hours, the temperature was decreased to about roomtemperature in about five hours. The preforms were removed from thefurnace, and it was observed that the preforms had sintered and formed athree-dimensional rigidized structures.

A foam brush was utilized to apply a uniform coating of DAG® 154colloidal graphite {Acheson Colloids Co., Port Huron, Mich.) to the four1/2 inch (13 mm) thick sides and to one 3 inch (76 mm) square surface ofeach preform. The coating was allowed to dry and a second coating ofDAG® 154 colloidal graphite was applied to the five sides of eachpreform previously coated. Each preform was turned over and the finalside was coated with DAG® 154 colloidal graphite. However, before theDAG® 154 colloidal graphite could substantially dry, excess DAG® 154 wasremoved from the surface of the preform utilizing a paper towel. Asecond coating of DAG® 154 colloidal graphite was applied to the finalside of each preform and a paper towel was again used to remove excesscoating before it dried.

As shown in FIG. 5, a graphite boat 77 having internal dimensions ofabout 10 inches {254 mm) square by about 4 inches (102 mm) deep wasprepared by lining the bottom of the graphite boat 77 with a sheet ofGRAFOIL® graphite foil 71 (Union Carbide Company, Danbury, Conn.) havingdimensions of about 10 inches (254 mm) square by about 0.015 inch (0.38mm) thick. An about 1 inch (25 mm) thick layer of a bedding material 72comprising by weight about 971/2% 90 grit E1ALUNDUM® alumina (NortonCompany, Worcester, Mass.) and about 21/2% F-69 borosilicate glass frit(Fusion Ceramics, Inc., Carrollton, Ohio) was poured into the graphiteboat 77 and onto the GRAFOIL® sheet 71. A foam brush was used toestablish a level layer of bedding material 72. A matrix metal ingot 73having dimensions of about 7 inches (178 mm) square by about 1/2 inch(13 mm) high, weighing about 1003 grams and comprising by weight about15% silicon, 5% magnesium and the balance aluminum, was placed into thegraphite boat 77 and onto the bedding material 72. Four equally spacedsquare holes measuring about 27/8 inches (73 mm) square were cut in aGRAFOIL® graphite foil sheet having dimensions of about 7 inches (178mm) square by about 0.015 inch (0.38 mm) thick. The GRAFOIL® sheet 74was placed into the graphite boat 77 and centered over the matrix metalingot 73. A total of about 1.8 grams of -50 mesh atomizod magnesium 76(Hart Corporation, Tamaqua, Pa.) was evenly dispersed throughout thefour holes in the GRAFOIL® sheet 74. The four preforms 75 were centeredover the four holes in the GRAFOIL® sheet 74 such that the final side(as identified above) of each of the preforms was in contact with themagnesium layer 76.

The graphite boat 77 and its contents were placed into a resistanceheated controlled atmosphere furnace at about room temperature. Thefurnace was sealed, evacuated to about 30 inches (762 mm) of mercuryvacuum, and backfilled with nitrogen gas to about atmospheric pressure.A nitrogen gas flow rate of about 5 liters per minute was establishedwithin the furnace. The temperature in the furnace was increased fromabout room temperature to about 200° C. at a rate of about 200° C. perhour. After maintaining a temperature of about 200° C. for about sixhours, the temperature in the furnace was increased to about 550° C. ata rate of about 200° C. per hour. After maintaining a temperature ofabout 550° C. for about two hours, the temperature in the furnace wasincreased to about 875° C. at a rate of about 200° C. per hour. Aftermaintaining a temperature of about 875° C. for about 30 hours, thetemperature in the furnace was decreased to about 700° C. at a rate ofabout 200° C. per hour. The graphite boat 77 and its contents were thenremoved from the furnace. An approximately 10 inch (254 mm) square sheetof FIBERFRAX® 907-J fiber insulation paper (The Carborundum Company,Niagara Falls, N.Y.) was placed onto a graphite table. The graphite boat70 and its contents were placed on top of the FIBERFRAX® insulationmaterial and allowed to cool to room temperature. Upon reaching roomtemperature, the formed metal matrix composite bodies were easilyremoved from the solidified carcass of matrix metal by inverting thesolidified carcass of matrix metal and applying light hammer blows tothe bottom of the carcass of matrix metal.

EXAMPLE 6

This Example further demonstrates that a rigidized filler material maybe spontaneously infiltrated to yield a metal matrix composite body.

A metal matrix composite body was fabricated in substantially the samemanner as described in Example 5 except that the filler material mixturecomprised about 1750, grams of 220 grit 39 CRYSTOLON® green siliconcarbide particulate (Norton Company, Worcester, Mass.); about 250 gramsof 500 grit 39 CRYSTOLON® green silicon carbide particulate; about 250grams of 800 grit 39 CRYSTOLON® green silicon carbide particulate; andabout 250 grams of 1000 grit 39 CRYSTOLON® green silicon carbideparticulate.

All other procedures for fabricating the metal matrix composite bodiesin this Example were substantially the same as described in Example 5.The formed metal matrix composite bodies were easily removed from thesolidified matrix metal in a manner substantially identical to themanner described in Example 5.

EXAMPLE 7

This Example further demonstrates that a rigidized preform may bespontaneously infiltrated to yield a highly loaded metal matrixcomposite body. Specifically, an aqueous solution of BLUONIC® Acolloidal alumina (Wesbond Corp., Wilmington, Del.) weighing about 201grams was diluted with about 399 grams of deionized water and placedinto a one (1) gallon plastic jar (VWR Scientific, Bridgeport, N.J.).About 1400 grams of 500 grit 39 CRYSTOLON® green silicon carbideparticulate (Norton Company, Worcester, Mass.) and about 600 grams of1000 grit 39 CRYSTOLON® green silicon carbide particulate were added tothe jar. About 2 ml of Colloids 581B defoamer (Colloids, Inc., Newark,N.J.) were then added to the jar to prepare a slurry for sedimentcasting. A total of four (4) jars were prepared in this manner. Theslurries were roll mixed for at least about 5 hours on a jar mill. AGrade GI-1000 silicone rubber mold (Plastic Tooling Supply Co., Exton,Pa.) having an internal cavity measuring about 7 inches (178 mm) squareand about 51/4 inches (133 mm) deep was cleaned with tap water and barsoap to remove any dirt or other debris from the mold, and the mold wasplaced onto a flat rigid aluminum plate. The mold/plate assembly wasthen placed onto a level vibrating table. The vibrating table was turnedon and approximately 31/2 jars of the slurry were poured into the moldin a smooth and continuous manner. The mold and its contents weresubjected to vibration for at least about 1 hour to condense the slurryinto a preform, with excess surface liquid being removed with a sponge.The vibrating table was turned off and the mold/plate/preform assemblywas placed into a freezer. Residual water in the preform was permittedto freeze thoroughly, then the mold/plate/preform assembly was removedfrom the freezer and the frozen sediment cast preform, having dimensionsof about 7 inches (178 mm) square by about 31/2 inches (89 mm) thick,was removed from the mold. The preform was then placed onto a refractorysupport plate, which had been covered with a sheet of FIBERFRAX® 970-Jfiber insulation paper (McNeil Refractories, Easton, Pa.). The supportedpreform was placed into a resistance heated air atmosphere furnace. Thefurnace temperature was raised from substantially room temperature toabout 85° C. in about 1/2 hour. After maintaining a temperature of about85° C. for about 24 hours, the temperature was then increased from about85° C. to about 1050° C. in a period of about 10 hours. Aftermaintaining a temperature of about 1050° C. for about 2 hours, thetemperature was decreased to about room temperature in a period of about10 hours. The preform was removed from the furnace, and it was observedthat the preform had sintered and formed a three-dimensional rigidizedstructure.

As shown in cross-section in FIG. 6, a graphite foil box 41 measuringabout 111/2 inches (292 mm) by about 81/2 inches (216 mm), and about71/2 inches (191 mm) high, was fabricated from a single sheet ofGRAFOIL® graphite foil (Union Carbide Company, Danbury, Conn.) measuringabout 0.015 inch (0.38 mm) thick by making strategically located cutsand folds in the sheet. The folds in the GRAFOIL® sheet were cementedtogether with RIGIDLOCK® graphite cement (Polycarbon Corporation,Valencia, Calif.). Strategically placed staples helped to reinforce thegraphite cement. The GRAFOIL® box 41 was then placed within a graphiteboat 40 having inner dimension which were substantially the same as thedimensions of the GRAFOIL® box 41. The fired preform 42 was then placedinto the bottom of the GRAFOIL® box 41. An approximately 1 to 2 particlethick layer of -100 mesh magnesium powder 43 (high purity grade, 99.98,Hart Corporation, Tamaqua, Pa.) was sprinkled evenly over the topsurface of the fired preform 42.

A gating means for controlling the supply of matrix metal whichcontacted the preform was constructed in the following manner. A sheetof GRAFOIL® 44 measuring about 7 inches (178 mm) square was prepared bycutting an approximately 6 inch (152 mm) diameter hole in the center ofthe sheet. A graphite riser ring 45 measuring about 3/8 inch (10 mm)high and about 6 inches (152 mm) in inside diameter was cemented to theGRAFOIL® sheet 44 using RIGIDLOCK® graphite cement (PolycarbonCorporation, Valencia, Calif.) such that the inside diameter of the ring45 substantially coincided with the hole in the GRAFOIL® sheet 44. Thegating means, comprising the GRAFOIL® sheet 44 and the graphite riserring 45, was then placed into the graphite boat 40 on top of the layerof magnesium powder 43 and oriented such that the GRAFOIL® sheet 44contacted the magnesium powder layer 43 and the graphite riser ring 45was on a top surface of the GRAFOIL® sheet 44. The graphite riser ring45 was then filled to about half of its height with an admixture 46comprising by weight about 98 percent (comprising about 70 percent 54grit and about 30 percent 90 grit) 39 CRYSTOLON® green silicon carbideparticulate (Norton Company, Worcester, Mass.) and about 2 percent -325mesh magnesium powder (Hart Corporation). The remaining portion of thegraphite riser ring 45 was filled with -100 mesh magnesium powder 47.The riser ring 45 was then covered with a circular sheet of aluminumfoil 48 having a diameter measuring about 1/4 inch (6 mm) larger thanthe outside diameter of the graphite riser ring 45. A bedding materialadmixture 49 comprising by weight about 1500 grams of equal parts 90grit, 220 grit, and 500 grit E1ALUNDUM® alumina (Norton Company) andabout 225 grams of F69 glass frit (Fusion Ceramics, Inc., Carrollton,Ohio) was poured into the graphite boat 40 to a level substantiallyflush with the top of the graphite riser ring 45. Excess loose beddingmaterial 49 was then carefully removed from the aluminum foil cover 48.A matrix metal ingot 39 weighing about 5286 grams and comprising byweight about 15 percent silicon, about 5 percent magnesium and thebalance aluminum, was placed into the graphite boat 40 and centered overthe graphite riser ring 45 to form a lay-up. Additional bedding material49 was added around the matrix metal until the ingot 39 was covered withan about 1/2 inch (13 mm) layer of bedding material 49.

The graphite boat 40 and its contents were then placed into a resistanceheated controlled atmosphere furnace at substantially room temperature.The furnace was sealed, evacuated to about 30 inches (762 mm) of mercuryvacuum, and backfilled with nitrogen gas to about atmospheric pressure.A nitrogen gas flow rate of about 5 liters per minute was establishedwithin the furnace. The temperature in the furnace was then increased toabout 200° C. in about 1 hour. After maintaining a temperature of about200° C. for about 24 hours, the furnace temperature was then increasedto about 800° C. at a rate of about 200° C. per hour. After maintaininga temperature of about 800° C. for about 60 hours, the temperature wasthen decreased to about 700° C. at a rate of about 200° C. per hour. Ata temperature of about 700° C., the furnace was opened and the graphiteboat 40 and its contents were removed and placed onto a water cooledaluminum quench plate. The top and sides of the graphite boat 40 werecovered with an approximately 2 inch (51 mm) thick layer of CERABLANKET®ceramic fiber insulation material (Manville Refractory Products, Denver,Colo.) to assist in the directional solidification of the matrix metal.At room temperature, the assembly was disassembled to reveal that thematrix metal had spontaneously infiltrated the rigidized preform.

EXAMPLE 8

This Example further demonstrates that a rigidized preform may bespontaneously infiltrated to yield a highly loaded metal matrixcomposite body.

Sample A

An aqueous solution of BLUONIC® A colloidal alumina (WesbondCorporation, Wilmington, Del.) weighing about 201 grams was diluted withabout 399 grams of deionized water and placed into a one gallon plasticjar (VWR Scientific, Bridgeport, N.J.). About 1400 grams of 220 grit 39CRYSTOLON® green silicon carbide particulate (Norton Company, Worcester,Mass.) and about 600 grams of 500 grit 39 CRYSTOLON® green siliconcarbide particulate were added to the jar. About 2 ml of Colloids 581Bdefoamer (Colloids, Inc., Newark, N.J.) were then added to the jar toprepare a slurry for sediment casting. A total of two (2) jars wereprepared in this manner. The slurries were roll mixed for at least about5 hours on a jar mill. A Grade GI-1000 silicone rubber mold (PlasticTooling Supply Company, Exton, Pa.) having an internal cavity measuringabout 7 inches (178 mm) square and about 21/4 inches (57 mm) deep wascleaned with tap water and bar soap to remove any dirt or other debrisfrom the mold, and the mold was placed onto a flat rigid aluminum plate.The mold/plate assembly was then placed onto a level vibrating table.The vibrating table was turned on and approximately 11/2 jars of theslurry were poured into the mold in a smooth and continuous manner. Themold and its contents were subjected to vibration for at least about 1hour to condense the slurry into a preform, with excess surface liquidbeing removed with a sponge. The vibrating table was turned off and themold/plate/preform assembly was placed into a freezer. Residual water inthe preform was permitted to freeze thoroughly, then themold/plate/preform assembly was removed from the freezer and the frozensediment cast preform, having dimensions of about 7 inches (178 mm)square by about 11/2 inch (38 mm) thick, was removed from the mold. Thepreform was then placed onto a refractory support plate, which had beencovered with a sheet of FIBERFRAX® 970-J fiber insulation paper (McNeilRefractories, Easton, Pa.). The supported preform was placed into aresistance heated air atmosphere furnace. The furnace temperature wasraised from substantially room temperature to about 85° C. in about 1/2hour. After maintaining a temperature of about 85° C. for about 24hours, the temperature was then increased from about 85° C. to about1050° C. in a period of about 10 hours. After maintaining a temperatureof about 1050° C. for about 2 hours, the temperature was decreased toabout room temperature in a period of about 10 hours. The preform wasremoved from the furnace, and it was observed that the preform hadsintered and formed a three-dimensional rigidized structure.

As shown in cross-section in FIG. 7, a graphite foil box 91 measuringabout 81/2 inches (216 mm) square and about 4 inches (102 mm) high wasfabricated from a single sheet of GRAFOIL® graphite foil (Union CarbideCompany,. Danbury, Conn.) measuring about 0.015 inch (0.38 mm) thick bymaking strategically located cuts and folds in the sheet. The folds inthe GRAFOIL® sheet were cemented together with RIGIDLOCK® graphitecement (Polycarbon Corporation, Valencia, Calif.). Strategically placedstaples helped to reinforce the graphite cement. The GRAFOIL® box 91 wasthen placed within a graphite boat 90, having inner dimensions whichwere substantially the same as the dimensions of the box 91. The firedpreform 92 was then placed into the bottom of the GRAFOIL® box 91. Anapproximately 1 to 2 particle thick layer of -100 mesh magnesium powder93 (high purity grade, 99.98, Hart Corporation, Tamaqua, Pa.) wassprinkled evenly over the top surface of the fired preform 92.

A gating means for controlling the supply of matrix metal which contactsthe preform 92 was constructed in the following manner. A sheet ofGRAFOIL® 94 measuring about 7 inches (178 mm) square was prepared bycutting an approximately 21/2 inch diameter hole in the center of thesheet. Over the hole, a graphite riser ring 95 measuring about 3/8 inch(10 mm) high and about 21/2 inches (64 mm) in inside diameter wascemented to the GRAFOIL® sheet 94 using RIGIDLOCK® graphite cement(Polycarbon Corporation) such that the inside diameter of the ring 95substantially coincided with the hole in the GRAFOIL® sheet 94. Thegating means, comprising the GRAFOIL® sheet 94 and the graphite riserring 95, was then placed into the graphite boat 90 on top of the layerof magnesium powder 93 and oriented such that the GRAFOIL® sheet 94contacted the magnesium powder layer 93 and the graphite riser ring 95was on a top surface of the GRAFOIL® sheet 94. The graphite riser ring95 was then filled with -100 mesh magnesium powder 96. The riser ring 95was then covered with a circular sheet of aluminum foil 97 having adiameter of about 1/4 inch (6 mm) larger than the outside diameter ofthe graphite riser ring 95. A bedding material admixture 98 comprisingby weight about 1500 grams of equal parts 90 grit, 220 grit, and 500grit E1ALUNSUM® alumina (Norton Company, Worcester, Mass.) and about 225grams of F69 glass frit (Fusion Ceramics, Inc., Cleveland, Ohio) waspoured into the graphite boat 90 to a level substantially Rush the topof the graphite riser ring 95. Loose bedding material 98 was thencarefully removed from the aluminum foil cover 97. A matrix metal ingot99 weighing about 2341 grams and comprising by weight about 15% silicon,about 5% magnesium, and the balance aluminum, was placed the graphiteboat 90 and centered over the graphite riser ring 95 to form a lay-up.

The graphite boat 90 and its Contents were then placed into a resistanceheated controlled atmosphere furnace at substantially room temperature.The furnace was sealed, evacuated to about 30 inches (762 mm) of mercuryvacuum, and backfilled with nitrogen gas to about atmospheric pressure.A nitrogen gas flow rate of about 4 liters per minute was established inthe furnace. The temperature in the furnace was then increased to about250° C. at a rate of about 200° C. per hour. After maintaining atemperature of about 250° C. for about 391/2 hours, the furnacetemperature was then increased to about 825° C. at a rate of about 150°C. per hour. After maintaining a temperature of about 825° C. for about20 hours, the temperature was then decreased to about 675° C. at a rateof about 200° C. per hour. At a temperature of about 675° C., thefurnace was opened and the graphite boat 90 and its contents wereremoved and placed onto a water cooled aluminum quench plate. FEEDOL®No. 9 hot topping particulate mixture (Foseco, Inc., Cleveland, Ohio)was poured onto the residual molten matrix metal reservoir todirectionally solidify the matrix metal in the metal matrix compositebody. After the bulk of the exothermic hot topping reaction hadsubsided, the top and sides of the graphite boat 90 were covered with anapproximately 2 inch (51 mm) thick layer of CERABLANKET® ceramic fiberinsulation material (Manville Refractory Products, Denver, Colo.) toassist in the directional solidification of the matrix metal. At roomtemperature, the assembly was disassembled to reveal that the matrixmetal had spontaneously infiltrated the rigidized preform.

Sample B

A metal matrix composite body was fabricated in essentially the samemanner as described in Sample A. The formed metal matrix composite bodywas sectioned into test coupons and mechanical property data wasobtained by the following procedures.

Measurement of Four Point Flexural Strength

The four point flexural strength of the metal matrix composite materialwas determined using MIL-STD-1942A, Flexural Strength of HighPerformance Ceramics at Ambient Temperature. Rectangular flexuralstrength test specimens having dimensions of about 2 inches (51 mm) longby about 0.24 inch (6 mm) wide by about 0.12 inch (3 mm) thick wereused. Test Figure configuration B as outlined in Section 5.2 ofMIL-STD-1942A was employed. The four point test fixture was then placedonto the base of Model No. CITS 2000/6 universal testing machine (SystemIntegration Technology, Inc., Stoughton, Mass.) having a 500 lb (2225 N)full scale deflection load cell. A computer data acquisition system wasconnected to the measuring unit and strain gauges in the load cellrecorded the test responses. The flexural strength test specimens weredeformed at a constant cross-head travel rate of about 0.51 millimetersper minute. The flexural strength and the maximum strain to failure werecalculated from the sample geometry and recorded responses with programsfrom within the computer.

Measurement Of Ultimate Tensile Strength (U.T.S.)

The tensile strength was determined using ASTM #B557-84 "StandardMethods of Tension Testing Wrought and Cast Aluminum and MagnesiumProducts". The geometry of the pin-loaded tensile bar is shown in FIG.6. The strain of the pin-loaded tension test specimen was measured withstrain gauges (350 ohm bridges) designated CEA-06-375UW-350 fromMicromeasurements of Raleigh, N.C. The tensile test bar was placed intothe gripping fixture on a Syntec 5000 pound (2269 kg) load cell(Universal Testing Machine, Model No. CITS 2000/6 manufactured by SystemIntegration Technology Inc., of Straton, Mass.). A computer dataacquisition system was connected to the measuring unit, and the straingauges recorded the test responses. The test specimen was deformed at aconstant rate of 0.020 inches/minute (0.508 mm/minute) to failure. Themaximum stress, maximum strain and strain to failure were calculatedfrom the sample geometry and recorded responses with programs within thecomputer.

Measurement of Elastic Modulus by the Resonance Method

The elastic modulus of the metal matrix composite was determined by asonic resonance technique which is substantially the same as ASTM methodC848-88. Specifically, a composite sample measuring from about 1.8 to2.2 inches long, about 0.24 inches wide and about 1.9 inches thick(about 45 mm to about 55 mm long, about 6 mm wide and about 4.8 mmthick) was placed between two transducers isolated from room vibrationsby an air table supporting a granite stone. One of the transducers wasused to excite frequencies within the composite sample while the otherwas used to monitor the frequency response of the metal matrixcomposite. By scanning through frequencies, monitoring and recording theresponse levels for each frequency and noting the resonant frequency,the elastic modulus was determined.

Measurement of the Fracture Touqhness for Metal Matrix Composite Using aChevron Notch Specimen

The method of Munz, Shannon and Bubsey, was used to determine thefracture toughness of metal matrix composite. The fracture toughness wascalculated from the maximum load of Chevron notch specimen in four pointloading. Specifically, the geometry of the Chevron notch specimen wasabout 1.8 to 2.2 inches (45 to 55 mm) long, about 0.19 inches (4.8 mm)wide and about 0.24 inches (6 mm) high. A Chevron notch was cut with adiamond saw to propagate a crack through the sample. The Chevron notchedsamples, the apex of the Chevron pointing down, were placed into afixture within a Universal test machine. The notch of the Chevron notchsample, was placed between two pins 1.6 inches (40 mm) apart andapproximately 0.79 inch (20 mm) from each pin. The top side of theChevron notch sample was contacted by two pins 0.79 inch (20 mm) apartand approximately 0.39 inch (10 mm) from the notch. The maximum loadmeasurements were made with a Sintec Model CITS-2000/6 Universal TestingMachine manufactured by System Integration Technology Incorporated ofStraton, Mass. A cross-head speed of 0.02 inches/minute (0.58millimeters/minute) was used. The load cell of the Universal testingmachine was interfaced to a computer data acquisition system. Chevronnotch sample geometry and maximum load were used to calculate thefracture toughness of the material. Several samples were used todetermine an average fracture toughness for a given material.

Measurement of Apparent Density

The apparent density of a sample is measured by first insuring that thesample is completely dry. The mass of the sample is determined asaccurately as possible. The sample is then placed into the samplechamber of an AccuPyc 1330 Autopycnometer (Micromeritics, Inc.,Norcross, Ga.). The autopycnometer automatically calculates the apparentvolume of the sample. Apparent density is found by simply dividing theapparent volume into the mass.

The mechanical properties of the formed metal matrix composite body ofthis Sample B are listed in Table I.

                  TABLE I                                                         ______________________________________                                        MECHANICAL PROPERTIES FOR METAL MATRIX                                        COMPOSITE BODY OF EXAMPLE 8, SAMPLE B                                         ______________________________________                                        Density (g/cc):       3.00                                                    Elastic Modulus (GPa):                                                                              270                                                     Four Point Flexural Strength (MPa):                                                                 316 ± 10                                             Fracture Toughness (MPa-m.sup.1/2):                                                                 11.0 ± 0.3                                           Ultimate Tensile Strength (MPa):                                                                    251 ± 11                                             ______________________________________                                    

EXAMPLE 9

This Example demonstrates that rigidized preforms having a high volumefraction of filler material may be spontaneously infiltrated to formmetal matrix composite bodies. FIG. 8 shows a schematic cross-sectionalview of the setup used to produce the metal matrix composite of thisExample, as described below. Specifically, a steel mold 250 wasprepared, having an inner cavity measuring about 6 inches (152 mm) longby about 6 inches (152 mm) wide by about 6 inches (152 mm) deep. Thebottom surface of the steel mold 250 was covered with a piece ofgraphite foil 251 (Grafoil® from Union Carbide), having dimensions ofabout 3 inches (76 mm) long by about 3 inches (76 ram) wide by about0.015 inches (0.38 mm) thick. A commercially available sintered siliconcarbide preform 252 (obtained from I Squared R Element, Inc., Akron,N.Y.), having an outer diameter of about 1.75 inches (45 mm) add aninner diameter of about 0.75 inches (19 mm) and cut to a length of about3 inches (76 mm), was wrapped in a piece of graphite foil 253 and placedonto the graphite foil 251 in the steel box 250. A 90 grit aluminamaterial 254 (38 Alundum, Norton Company, Worcester, Mass.) was pouredinto the space between the silicon carbide preform 252 and the steelmold 250. The inner cavity of the silicon carbide preform wassubstantially filled with graphite powder 255 (KS-44 from Lonza, Inc.,Fair Lawn, N.J.). A graphite foil box 256, measuring about 5.75 inches(146 mm) long by about 5.75 inches (146 mm) wide by about 3 inches (76mm) deep was constructed from a single sheet of GRAFOIL® graphite foil{Union Carbide Company, Danbury, Conn.) measuring about 0.015 inch (0.38mm) thick by making strategically located cuts and folds in the sheet.The folds in the GRAFOIL® sheet were cemented together with RIGIDLOCK®graphite cement (Polycarbon Corporation, Valencia, Calif.).Strategically placed staples helped to reinforce the graphite cement. Ahole 257, measuring about 1.75 inches (43 mm) in diameter andcorresponding to the outer diameter of the silicon carbide preform 252,was cut into the bottom of the graphite foil box 256 and the graphitefoil box 256 was placed around the top of the silicon carbide preform252 in the steel mold 250. A -100 mesh magnesium powder material 258(Hart Corporation, Tamaqua, Pa.) was placed on the top surface of thesilicon carbide preform 252 extending into the graphite foil box 256. Amatrix metal 259 comprising by weight 12 percent silicon, 6 percemagnesium and the balance aluminum, was placed into the graphite foilbox 256 contained within the steel mold 250.

The steel mold 250 and its contents were placed into a room temperatureretort lined resistance heated furnace. The retort door was closed, andthe retort was evacuated to at least 30 inches (762 mm) Hg. After thevacuum was reached, nitrogen was introduced into the retort chamber at aflow rate of about 3 liters/minute. The retort lined furnace was thenheated to about 800° C. at a rate of about 200° C./hour and held forabout 10 hours at about 800° C. with a flowing nitrogen atmosphere ofabout 3 liters/minute. The retort lined furnace was then ramped fromabout 800° C. to about 675° C. at a rate of about 200° C./hour. At about675° C., the steel mold 250 and its contents were removed from theretort and placed onto a room temperature graphite plate todirectionally solidify the metal matrix composite and the carcass ofresidual matrix metal. At room temperature, the assembly wasdisassembled to reveal that the matrix metal had spontaneouslyinfiltrated the rigidized preform.

EXAMPLE 10

This Example demonstrates that a rigidized preform can be infiltrated byspontaneous infiltration to produce a metal matrix composite. The setupfor the spontaneous infiltration is shown schematically in FIG. 9.

A stainless steel container 260 measuring about 4 inches (102 mm) squareby about 3 inches (76 mm) tall was lined with GRAFOIL® graphite foil(Union Carbide Company, Danbury Conn.). Specifically, a sheet ofGRAFOIL® about 15 mils thick was cut and folded to form a box ofsubstantially the same size and shape as the inner dimensions of thestainless steel container 260. The folds in the GRAFOIL® sheet werecemented together with RIGIDLOCK® graphite cement (PolycarbonCorporation, Valencia, Calif.) to help maintain the shape of theGRAFOIL® box. Furthermore, the box was stapled together at strategiclocations to reinforce the graphite cement.

About 153 grams of a blend of green silicon carbide particulates with amaximum particle size of about 70 microns was injection molded, byTechnical Ceramic Laboratories, Inc., Alpharetta, Ga., using a suitablebinder and other injection molding additives to form a preform 264measuring about 21/4 inches (57 mm) in diameter and about 1 inch (25 mm)thick. The concentration of silicon carbide in the injection moldedpreform 264 amounted to about 70 volume percent.

Grade C-75 unground alumina (Alcan Chemicals Division of AluminumCompany of Canada Limited, Montreal, Quebec, Canada) was poured onto arefractory plate measuring about 11 inches (279 mm) long by about 6inches (152 mm) wide by about 1 inch (25 mm) thick to a depth of about1/2 inch (13 mm) and leveled. The injection molded preform was thenplaced on top of the layer of alumina particulate. The refractory plateand its contents were then placed into a resistance heated airatmosphere furnace at substantially room temperature. The furnacetemperature was then increased to about 1050° C. over a period of about24 hours. After maintaining a temperature of about 1050° C. for about 2hours, power to the furnace was turned off and the furnace was allowedto cool back to room temperature. When the furnace chamber had reachedsubstantially room temperature, the refractory plate and its contentswere removed from the furnace revealing that the organic constituents inthe injection molded preform had volatilized or had combusted and thatthe surfaces of the silicon carbide particles had oxidized to silica(SiO₂) which fused the particles to one another at contact pointsbetween particles to produce a rigidized preform.

An admixture of bedding material 266 comprising by weight about 15percent Grade P 54P borosilicate glass frit (Inorganic ChemicalsDivision, Mobay Chemical Corporation, Baltimore, Ohio) and the balanceequal parts by weight of 90 grit, 220, grit and 500 grit E1ALUNDUM®fused alumina (Norton Company) was poured into the GRAFOIL® lined steelcontainer 260 to a depth of about 1/4 inch (6 mm) and leveled. The firedpreform 264 was placed into the GRAFOIL® lined steel container 260 andcentered in the steel container on top of the bedding material admixture266. A graphite riser ring gating means 268 having an outer diameter ofabout 11/2 inches (38 mm) and an inner diameter of about 1 inch (25 mm)and measuring about 3/8 inch (10 mm) tall was centered on the top of thepreform 264. Additional bedding material admixture 266 was poured intothe steel container around the preform and the graphite riser ring 268to a level of about 1/8 inch (3 mm) from the top of the graphite ring,and was then leveled. A GRAFOIL® box 262, having substantially the samedimensions as the GRAFOIL® liner in the stainless steel container 260was fabricated by strategically cutting and folding a GRAFOIL® sheet,cementing the folds with RIGIDLOCK® graphite cement (PolycarbonCorporation, Valencia, Calif.) and stapling the GRAFOIL® box toreinforce the RIGIDLOCK® cement. An approximately 1 inch (25 mm)diameter hole was cut into the center of the bottom of the GRAFOIL® box262 such that when the GRAFOIL® box 262 was placed into the steelcontainer 260 the hole substantially lined up with the inner diameter ofthe graphite riser ring 268. With the GRAFOIL®box 262 in the steelcontainer 260 and centered over the graphite riser ring 268, the top ofthe GRAFOIL® box 262 was trimmed such that the top of the GRAFOIL® boxwas of substantially the same height as the steel container. About 3grams of magnesium particulate 270 (-100 mesh, Hart Corporation,Tamaqua, Pa.) was poured into the space inside the graphite riser ring268 and leveled. A matrix metal ingot 272 measuring about 3/4 inch (19mm) square by about 1 inch (25 mm) thick weighing about 460 grams andcomprising by weight about 12 percent silicon, 6 percent magnesium, andthe balance commercially pure aluminum, was placed into the GRAFOIL® box262 and centered over the hole in the bottom of the box to form alay-up.

The steel container 260 and its contents were then placed onto agraphite catcher plate 274 measuring about 14 inches (356 mm) long byabout 101/4 inches (260 mm) wide by about 1 inch (25.4 mm) tall andhaving a wall thickness of about 1/4 inch (6 mm). The graphite catcherplate 274 and its contents were then placed into an electric resistanceheated controlled atmosphere furnace (retort). The retort was sealed,evacuated to about 30 inches (762 mm) of mercury vacuum, and thenbackfilled with nitrogen gas to substantially atmospheric pressure. Anitrogen gas flow rate of about 4 liters per minute was established. Thetemperature in the retort was then increased from substantially roomtemperature to a temperature of about 850° C. at a rate of about 200° C.per hour. After maintaining a temperature of about 850° C. for about 15hours, the temperature was then decreased to about 760° C. at a rate ofabout 200° C. per hour. At a temperature of about 760° C., the graphitecatcher plate 274 and its contents were removed from the retort andplaced onto a water cooled aluminum quench plate to directionallysolidify the matrix metal. FEEDOL® No. 9 hot topping particulate mixturewas poured on top of the molten matrix metal reservoir 272. After thebulk of the exothermic reaction had subsided, an approximately 2 inch(51 mm) thick layer of CERABLANKET® ceramic fiber insulation (ManvilleRefractory Products, Denver, Colo.) was placed over the top and aroundthe sides of the steel container 260. After cooling to substantiallyroom temperature, the lay-up was removed from the steel container 260and the bedding material admixture 266 was removed with light hammerblows to reveal that the matrix metal 272 had infiltrated of the preform264 to produce a metal matrix composite. Thus, this Example illustratesthat a rigidized preform can be infiltrated using a spontaneousinfiltration process to produce a metal matrix composite.

EXAMPLE 11

This example further demonstrates that a rigidized preform can beinfiltrated by a molten matrix metal via a spontaneous infiltrationtechnique.

An aqueous solution of BLUONIC® A colloidal alumina (Wesbond Corp.,Wilmington, Del.) weighing about 200 grams was diluted with about 400grams of deionized water and placed into a one-gallon plastic jar(Fischer Scientific, Pittsburgh, Pa.). About 1400 grams of 220 grit 39CRYSTOLON® green silicon carbide particulate (Norton Company, Worcester,Mass.), about 600 grams of 500 grit 39 CRYSTOLON® green silicon carbideparticulate and about 2 ml of COLLOIDS 581-B defoamer (Colloids, Inc.,Newark, N.J.) were also added to the jar to prepare a slurry forsediment casting. The plastic jar and its contents were placed onto aroller mill and roll mixed for about 5 hours.

A grade GI-1000 silicone rubber mold (Plastic Tooling Supply Company,Exton, Pa.) having an internal cavity measuring about 3 inches (76 mm)square and about 1 inch (25 mm) deep was placed onto a flat rigidaluminum plate, and the mold and aluminum plate were placed on avibrating table. The vibrating table was turned on, and about 270 gramsof the slurry was poured into the rubber mold. The mold and slurry wasvibrated for about 1 hour to sediment cast the slurry into a preform,with excess water on the surface of the sediment cast preform beingremoved with a sponge. After vibrating the mold for about 1 hour, thevibrating table was turned off and the aluminum plate/mold assemblycontaining the sediment cast preform was removed from the vibratingtable and placed into a freezer. Residual water in the preform waspermitted to freeze thoroughly and the aluminum plate/mold assembly wasremoved from the freezer and the frozen sediment cast preform wasremoved from the mold.

An about 12 inch (305 mm) long by about 6 inch (152 mm) wide sheet ofFIBERFRAX® 907J fiber insulation paper (The Carborundum Company, NiagaraFalls, N.Y.) was placed onto a refractory plate having dimensions ofabout 12 inches (304 mm) long by about 6 inches (152 mm) wide by about 1inch (25 mm) thick and the preform was placed onto the fiber insulationpaper. The refractory plate/fiber insulation paper/preform assembly wasplaced within a room temperature air atmosphere furnace. The temperaturein the furnace was increased from about room temperature to about 85° C.in about 1 hour. After maintaining a temperature of about 85° C. forabout 10 hours, the temperature in the furnace was increased to about1050°C. in about 10 hours. After maintaining a temperature of about1050°0 C. for about 2 hours, the temperature in the furnace wasdecreased to about room temperature in about 5 hours. The refractoryplate/fiber insulation paper/preform assembly was removed from thefurnace. The preform was inspected, and it was observed that the preformhad sintered and formed a three-dimensional rigidized body.

Five sides of the preform were lightly spray coated with KRYLON® acrylicspray coating (Borden Inc., Columbus, Ohio). A mixture to be used as abarrier coating comprising by volume about 50% DAG® 154 colloidalgraphite (Acheson Colloids, Port Huron, Mich.) and about 50% denaturedethanol was prepared. An air brush was used to apply a thin layer ofbarrier coating to the five sides of the preform previously coated withthe acrylic spray Coating. The barrier coating was allowed to dry. Atotal of three barrier coatings were applied in this manner.

As shown in FIG. 10, an about 1 inch (25 mm) layer of bedding material32 comprising by weight about 15% F-69 borosilicate glass frit (FusionCeramics, Inc., Carrollton, Ohio) and the balance equal proportions of90, 220 and 500 grit E1ALUNDUM® alumina (Norton Company, Worcester,Mass.) was poured into a graphite boat 30 having internal dimensions ofabout 10 inches (254 mm) square by about 4 inches (102 mm) high. Amatrix metal ingot 31 comprising by weight about 15% silicon,5%magnesium and the balance aluminum, was placed into the graphite boat30 and onto the bedding material 32. The matrix metal ingot 31 haddimensions of about 31/4 inches (83 mm) by about 4 inches (102 mm) byabout 1/2 inch (13 mm) and weighed about 561 grams. Additional beddingmaterial 32 was poured into the graphite boat 30 to a levelsubstantially the same as that of the top portion of the matrix metalingot 31. An about 1 particle-thick layer of -50 mesh atomized magnesium33 (Hart Corporation, Tamaqua, Pa.) was sprinkled onto the top surfaceof the matrix metal ingot 31. The preform 35 was placed into thegraphite boat 30 so that the uncoated surface of the preform was incontact with the layer of -50 mesh atomized magnesium 33.

A graphite foil box 34 measuring about 31/2 inches (89 mm) by 7 inches(178 mm) by 2 inches (51 mm) high was fabricated from a single sheet ofGRAFOIL® graphite foil {Union Carbide Company, Danbury, Conn.) measuringabout 0.015 inch {0.38 mm) thick by making strategically located cutsand folds in the sheet. The folds in the GRAFOIL® sheet were cementedtogether with RIGIDLOCK® graphite cement (Polycarbon Corporation,Valencia, Calif.). Strategically placed staples helped to reinforce thegraphite cement. The GRAFOIL® box 34 was inverted and placed into thegraphite boat 30 over the preform 35. Light hand pressure was applied tothe GRAFOIL® box 34 to embed the walls of the box 34 in the beddingmaterial 32.

The graphite boat 30 and s contents were placed into a resistance heatedcontrolled atmosphere furnace at about room temperature. The furnace wassealed, evacuated to about 30 inches (762 mm) of mercury vacuum, andbackfilled with nitrogen gas to about atmospheric pressure. A nitrogengas flow rate of about 5 liters per minute was established within thefurnace. The temperature in the furnace was increased at a rate of about200° C. per hour to about 300° C. After maintaining a temperature ofabout 300° C. for about 2 hours, the temperature in the furnace wasincreased to about 800° C. in about 21/2 hours. After maintaining atemperature of about 800° C. for about 10 hours, the temperature in thefurnace was decreased to about 700° C. in about 1/2 hour. The furnacedoor was opened, the GRAFOIL® box 34 was removed and the now formedmetal matrix composite body was removed from the graphite boat 30. Themetal matrix composite body was placed onto a sheet of FIBERFRAX® 907Jfiber insulation paper (The Carborundum Company, Niagara Falls, N.Y.)and allowed to cool to room temperature.

EXAMPLE 12

An aqueous solution of BLUONIC® A colloidal alumina (Wesbond Corp.,Wilmington, Del.) weighing about 61.6 grams was diluted with about 122.6grams of deionized water and placed into a 16 ounce NALGENE® plastic jar(Nalge Company, Rochester, N.Y.). About 430.4 grams of 220 grit 39CRYSTOLON® green silicon carbide particulate (Norton Company, Worcester,Mass.), about 184.8 grams of 500 grit 39 CRYSTOLON® green siliconcarbide particulate and an amount of Dow experimental ceramic binderXUS40303.00 (Dow Chemical Company, Midland, Mich.), weighingapproximately 0.6 grams, were added to the jar to prepare a slurry forcasting. The jar and its contents were roller milled for about 2 hours,then the jar and its contents were placed on an orbital mixer and mixedfor about 2 hours, then removed.

A Grade GI-1000 silicone rubber mold (Plastic Tooling Supply Company,Exton, Pa.) having a circular internal cavity measuring about 6 inches(152 mm) in diameter by about 0.0635 inch (2 mm) deep was placed onto aflat rigid aluminum plate. The filler material slurry was poured intothe mold until the mold was substantially full. The aluminum plate/moldassembly and its contents were then placed within a vacuum chamber, anda vacuum of about 28 inches (711 mm) of mercury was established withinthe chamber. After about 2 minutes, atmospheric pressure wasre-established within the vacuum chamber and the aluminum plate/moldassembly and its contents were removed from the vacuum chamber. The moldand its contents were then placed on a Syntron magnetic vibrator (FHC,West Reading, Pa.) to form the slurry into a sediment cast preform. Thevibrating table was turned on and the control knob was set to about 5.After about 1 minute the control knob was turned down to about 3 and theslurry mixture was scraped towards the middle of the mold utilizing aplastic spatula. After about 4 minutes of vibration with the controlknob set at 3, residual water was scraped from the top of the slurrymixture, the vibrating table was turned off, and the preform within themold was allowed to dry at room temperature for about 3 hours.

The preform was removed from the mold and placed onto a zirconia platehaving dimensions of about 61/2 inches (165 mm) square by about 1/2 inch(13 mm) thick. The zirconia plate and preform were placed within a roomtemperature air atmosphere furnace. The temperature in the furnace wasincreased from about room temperature to about 100° C. in about 1 hour.After maintaining a temperature of about 100° C.for about 1 hour, thetemperature in the furnace was increased to about 1100° C. in about 8hours. After maintaining a temperature of about 1100° C. for about 2hours, the temperature in the furnace was decreased to about roomtemperature in about 5 hours. The zirconia plate and preform wereremoved from the furnace, and it was observed that the preform hadsintered and formed a three-dimensional rigidized structure.

A mixture to be used as a barrier coating comprising by volume about 50%DAG®154 colloidal graphite (Acheson Colloids Company, Port Huron, Mich.)and about 50% denatured ethanol was prepared. An air brush was used toapply a thin layer of barrier coating to one side of the preform. Thebarrier coating was allowed to dry and an additional thin layer ofbarrier coating was applied in substantially the same manner. Thisprocedure was repeated until about 0.28 grams of the barrier coating wasapplied.

As shown in FIG. 11, a graphite boat 1 having internal dimensions ofabout 9 inches (229 mm) square by about 4 inches (102 mm) high and awall thickness of about 1/2 inch (13 mm) was altered in the followingmanner. An about 81/2 inch (216 mm) by about 4 inch (102 mm) section wascut out of one side wall 2 of the graphite boat 1. An about 3/16 (5 mm)inch thick groove was cut into the bottom portion and side portions ofthe graphite boat 1 to accommodate a sliding door mechanism. A graphiteplate 3 measuring about 9 inches (229 mm) wide by about 6 inches (152mm) high and having a thickness of about 3/16 inch (5 mm) was placedinto the grooves to form the sliding door mechanism. The inner surfacesof a portion of the graphite boat 1 were lined with a single sheet ofGRAFOIL® graphite foil 4 (Union Carbide Company, Danbury, Conn.)measuring about 0.015 inch (0.4 mm) thick by making strategicallylocated cuts and folds in the sheet. The folds in the GRAFOIL® sheetwere cemented together with RIGIDLOCK® graphite cement (PolycarbonCorporation, Valencia, Calif.). The sliding gate mechanism was leftunlined. A second graphite boat having internal dimensions of about 11/2inches (38 mm) by about 8 inches (203 mm) and a wall thickness of about1/2 inch (13 mm) was placed into the graphite boat 1 next to the wallopposite the sliding door mechanism. Four holes 6 measuring about 5/16inch (8 mm) in diameter were drilled through the bottom portion of theside wall of the second graphite boat 5 facing the sliding doormechanism. Six graphite riser rings 7 measuring about 1/4 inch (6 mm)high and having diameters of about 3/4 inch (19 mm) were strategicallyplaced into the first graphite boat 1 to act as a support means for thepreform. The graphite riser rings 7 were glued to the GRAFOIL® sheetutilizing GRAPHIBOND™ 551-R graphite cement (Aremco Products, Inc.,Ossining, N.Y.).

The preform 8 was placed onto the graphite riser rings 7 within thegraphite boat 1 such that the uncoated side of the preform 8 contactedthe graphite riser rings 7. A matrix metal ingot 9 comprising by weightabout 15% silicon, 5.5% magnesium and the balance aluminum, and having atotal weight of about 1496.5 grams, was placed into the second graphiteboat 5. The graphite boat 1 and its contents were placed into aresistance heated controlled atmosphere furnace at about roomtemperature. The furnace was sealed, evacuated to about 30 inches (762mm) of mercury vacuum, and backfilled with nitrogen gas to aboutatmospheric pressure. This procedure was repeated a second time. Anitrogen gas flow rate of about 5 liters per minute was establishedwithin the furnace. The temperature in the furnace was increased at arate of about 200° C. per hour to a level of about 800° C. Aftermaintaining a temperature of about 800° C. for about 16 hours, thefurnace door was opened and the sliding door mechanism was pulled uputilizing a pair of stainless steel tongs to allow the remaining moltenmatrix metal drain into a steel boat containing sand. Aftersubstantially all of the remaining molten matrix metal had drained intothe sand, the sliding gate mechanism was returned to its originalposition and the furnace door was closed, and the furnace and itscontents were allowed to return to room temperature. The door was thenopened, the graphite boat 1 and its contents were removed from thefurnace and the formed metal matrix composite body was removed from thegraphite boat 1. Thus, this Example further demonstrates that arigidized preform can be infiltrated by a molten matrix metal by aspontaneous infiltration technique.

We claim:
 1. A method for making a metal matrix compositecomprising:providing at least one permeable mass of at least one filler;rigidizing said at least one permeable mass to form at least onerigidized mass by (1) at least one process selected from the groupconsisting of (a) mixing at least one colloidal oxide havingstrengthening characteristics with said at least one permeable mass and(b) heating said at least one permeable mass to a sufficient temperatureand holding at said temperature for a sufficient amount of time to atleast partially sinter at least one of said at least one colloidal oxidehaving strengthening effects and said at least one filler and (2) atleast partially surrounding said at least one permeable mass with atleast one precursor to at least one supportive structural refractorymaterial which contacts at least a portion of at least one exteriorsurface of said at least one permeable mass, causing said at least oneprecursor to at least one supportive structural refractory material tobecome at least one supportive structural refractory material; andspontaneously infiltrating at least a portion of said at least onerigidized mass with at least one molten matrix metal.
 2. The method ofclaim 1, wherein said at least one colloidal oxide having strengtheningeffects and said at least one permeable mass are heated prior to beingcontacted with at least one molten matrix metal.
 3. The method of claim2, wherein said heating results in an at least partiallythree-dimensionally interconnected at least one permeable mass.
 4. Themethod of claim 2, wherein said at least one colloidal oxide havingstrengthening effects comprises at least one of at least one colloidalalumina and at least one colloidal silica.
 5. The method of claim 1,wherein said at least one filler comprises at least one silicon carbideand said at least one silicon carbide is at least partially converted toat least one silicon oxide during said at least partially sintering. 6.The method of claim 1, wherein said at least one supportive structuralrefractory material surrounds a majority of said at least one permeablemass.
 7. The method of claim 6, wherein said at least one supportivestructural refractory material is formed by providing at least oneprecursor to said at least one supportive material on at least a portionof at least one exterior surface of sad at least one permeable mass andconverting said at least one precursor into said at least one supportivematerial prior to contacting at least one molten matrix metal with saidat least one permeable mass.
 8. The method of claim 6, wherein said atleast one supportive structural refractory material comprises at leastone material selected from the group consisting of steels, graphites,glass frits and colloidal oxides.
 9. The method of claim 1, wherein saidpermeable mass is rigidized by combining at least two of said at leastone process and at least partially surrounding said at least onepermeable mass with at least one supportive structural refractorymaterial which contacts at least a portion of at least one exteriorsurface of said at least one permeable mass.
 10. The method of claim 1,wherein said infiltrating comprises spontaneous infiltration.
 11. Themethod of claim 10, wherein at least one infiltration enhancer precursoris provided to at least one of said at least one permeable mass, said atleast one rigidized mass and said at least one molten matrix metal, andsaid at least one infiltration enhancer precursor is caused to react toform at least one infiltration enhancer in at least a portion of atleast one said at least one permeable mass and said at least onerigidized mass.
 12. The method of claim 11, wherein said at least oneinfiltration enhancer precursor reacts with at least one infiltratingatmosphere.
 13. The method of claim 12, wherein said at least oneinfiltrating atmosphere is present for only a portion of theinfiltrating process.
 14. The method of claim 1, wherein said at leastone colloidal oxide is initially present in said at least one permeablemass in an amount of about 1-15 percent by weight.
 15. The method ofclaim 1, wherein said at least one permeable mass comprises at least oneceramic material.
 16. The method of claim 1, wherein said at least onematrix metal comprises aluminum.
 17. A method for making a metal matrixcomposite comprising:providing at least one permeable mass comprising atleast one filler; at least partially surrounding said at lest onepermeable mass with at least one precursor to at least one supportivestructural refractory material which contacts at least a portion of atleast one exterior surface of said at lest one permeable mass; providingat least one matrix metal; providing at least one material comprising atleast one of at least one infiltration enhancer precursor and at leastone infiltration enhancer to at least one of said at least one permeablemass and said at least one matrix metal; providing at least oneinfiltrating atmosphere; causing said at least one precursor to at leastone supportive structural refractory material to become at least onesupportive structural refractory material; causing said at least onematrix metal to become molten; and spontaneously infiltrating at least aportion of said at least one permeable mass.
 18. The method of claim 17,further comprising heating of said at least one permeable mass therebyresulting in an at least partially three-dimensionally interconnected atleast one permeable mass.
 19. The method of clam 17, further comprisingproviding at least one colloidal oxide comprising at least one materialselected from the group consisting of at least one colloidal alumina andat least one colloidal silica to said at least one permeable mass.
 20. Ametal matrix composite body made according to claim 17.